diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index a13e807029..774479e130 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -41,6 +41,10 @@ on:
   # allow calling from other repos in the ReactionMechanismGenerator organization
   workflow_call:
     inputs:
+      rmg-py-branch:
+        default: "main"
+        required: false
+        type: string
       rmg-db-branch:
         # if calling from RMG-database, must provide a branch
         required: true
@@ -52,23 +56,98 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
+# if running on RMG-Py but requiring changes on an un-merged branch of RMG-database, replace
+# main with the name of the branch
+env:
+  RMG_DATABASE_BRANCH: main
+
 jobs:
+  clone:
+    runs-on: ubuntu-latest
+    # skip scheduled runs from forks
+    if: ${{ !( github.repository != 'ReactionMechanismGenerator/RMG-Py' && github.event_name == 'schedule' ) }}
+    steps:
+      # Option 1: calling from branch on RMG/RMG-Py and using branch on RMG/RMG-database
+      - name: Checkout RMG-Py
+        if: github.repository == 'ReactionMechanismGenerator/RMG-Py'
+        uses: actions/checkout@v3
+        with:
+          repository: ReactionMechanismGenerator/RMG-Py
+          path: RMG-Py
+      - name: Checkout RMG-database
+        if: github.repository == 'ReactionMechanismGenerator/RMG-Py'
+        uses: actions/checkout@v3
+        with:
+          repository: ReactionMechanismGenerator/RMG-database
+          path: RMG-database
+          ref: ${{ env.RMG_DATABASE_BRANCH }}
+
+      # Option 2: calling from fork of RMG-Py and using branch on RMG/RMG-database
+      - name: Checkout RMG-Py
+        if: github.repository != 'ReactionMechanismGenerator/RMG-Py' && github.event.repository.name == 'RMG-Py'
+        uses: actions/checkout@v3
+        with:
+          repository: ${{ github.repository_owner }}/RMG-Py
+          path: RMG-Py
+      - name: Checkout RMG-database
+        if: github.repository != 'ReactionMechanismGenerator/RMG-Py' && github.event.repository.name == 'RMG-Py'
+        uses: actions/checkout@v3
+        with:
+          repository: ReactionMechanismGenerator/RMG-database
+          path: RMG-database
+          ref: ${{ env.RMG_DATABASE_BRANCH }}
+
+      # Option 3: calling from branch on RMG-database
+      - name: Checkout RMG-Py
+        if: github.repository == 'ReactionMechanismGenerator/RMG-database'
+        uses: actions/checkout@v3
+        with:
+          repository: ReactionMechanismGenerator/RMG-Py
+          path: RMG-Py
+          ref: ${{ inputs.rmg-py-branch }}
+      - name: Checkout RMG-database
+        if: github.repository == 'ReactionMechanismGenerator/RMG-database'
+        uses: actions/checkout@v3
+        with:
+          repository: ReactionMechanismGenerator/RMG-database
+          path: RMG-database
+          ref: ${{ inputs.rmg-db-branch }}
+
+      # Option 4: calling from fork on RMG-database
+      - name: Checkout RMG-Py
+        if: github.repository != 'ReactionMechanismGenerator/RMG-database' && github.event.repository.name == 'RMG-database'
+        uses: actions/checkout@v3
+        with:
+          repository: ${{ github.repository_owner }}/RMG-Py
+          path: RMG-Py
+          ref: ${{ inputs.rmg-py-branch }}
+      - name: Checkout RMG-database
+        if: github.repository != 'ReactionMechanismGenerator/RMG-database' && github.event.repository.name == 'RMG-database'
+        uses: actions/checkout@v3
+        with:
+          repository: ${{ github.repository_owner }}/RMG-database
+          path: RMG-database
+          ref: ${{ inputs.rmg-db-branch }}          
+
+      - name: Pass Repos to Build and Test
+        uses: actions/upload-artifact@v3
+        with:
+          name: repositories
+          path: ${{ github.workspace }}
+
   build-osx:
+    needs: clone
     runs-on: macos-latest
     # skip scheduled runs from forks
-    if: ${{ !( github.repository != 'ReactionMechanismGenerator/RMG-Py' && github.event_name == 'schedule' ) }}
-    env: 
-      # if running on RMG-Py but requiring changes on an un-merged branch of RMG-database, replace
-      # main with the name of the branch
-      RMG_DATABASE_BRANCH: main
     defaults:
       run:
         shell: bash -l {0}
     steps:
-      - name: Checkout RMG-Py
-        uses: actions/checkout@v3
+      - name: Fetch Repos
+        uses: actions/download-artifact@v3
         with:
-          repository: ReactionMechanismGenerator/RMG-Py
+          name: repositories
+          path: ${{ github.workspace }}
 
       # configures the mamba environment manager and builds the environment
       - name: Setup Mambaforge Python 3.7
@@ -87,19 +166,6 @@ jobs:
           mamba info
           mamba list
 
-      # Clone RMG-database
-      - name: Clone RMG-database - Reusable Workflow
-        if: github.repository == 'ReactionMechanismGenerator/RMG-database'
-        run: |
-          cd ..
-          git clone -b ${{ inputs.rmg-db-branch }} https://github.com/ReactionMechanismGenerator/RMG-database.git
-
-      - name: Clone RMG-database - RMG-Py
-        if: github.repository != 'ReactionMechanismGenerator/RMG-database'
-        run: |
-          cd ..
-          git clone -b $RMG_DATABASE_BRANCH https://github.com/ReactionMechanismGenerator/RMG-database.git
-
       # modify env variables as directed in the RMG installation instructions
       - name: Set Environment Variables
         run: |
@@ -114,24 +180,20 @@ jobs:
           make
 
   build-and-test-linux:
+    needs: clone
     runs-on: ubuntu-latest
-    # skip scheduled runs from forks
-    if: ${{ !( github.repository != 'ReactionMechanismGenerator/RMG-Py' && github.event_name == 'schedule' ) }}
-    env: 
-      # if running on RMG-Py but requiring changes on an un-merged branch of RMG-database, replace
-      # main with the name of the branch
-      RMG_DATABASE_BRANCH: main
-
+    env:
       # This is true only if this is a reference case for the regression testing:
       REFERENCE_JOB: ${{ github.ref == 'refs/heads/main' && github.repository == 'ReactionMechanismGenerator/RMG-Py' }}
     defaults:
       run:
         shell: bash -l {0}
     steps:
-      - name: Checkout RMG-Py
-        uses: actions/checkout@v3
+      - name: Fetch Repos
+        uses: actions/download-artifact@v3
         with:
-          repository: ReactionMechanismGenerator/RMG-Py
+          name: repositories
+          path: ${{ github.workspace }}
 
       # configures the mamba environment manager and builds the environment
       - name: Setup Mambaforge Python 3.7
@@ -150,19 +212,6 @@ jobs:
           mamba info
           mamba list
 
-      # Clone RMG-database
-      - name: Clone RMG-database - Reusable Workflow
-        if: github.repository == 'ReactionMechanismGenerator/RMG-database'
-        run: |
-          cd ..
-          git clone -b ${{ inputs.rmg-db-branch }} https://github.com/ReactionMechanismGenerator/RMG-database.git
-
-      - name: Clone RMG-database - RMG-Py
-        if: github.repository != 'ReactionMechanismGenerator/RMG-database'
-        run: |
-          cd ..
-          git clone -b $RMG_DATABASE_BRANCH https://github.com/ReactionMechanismGenerator/RMG-database.git
-
       # modify env variables as directed in the RMG installation instructions
       - name: Set Environment Variables
         run: |