Many thanks to all for the great conversation, I’ve refined and recreated a script that puts everything in the discussion here together (and a few more features like Grids Bubbles manipulation) with a Dynamo player UI (Revit 2020.2 + Dynamo 2.3):
You can find the script in the repo below ( ATnodes_Fit Grids to Viewport Crop Region.dyn)
https://github.com/alitehami/ATnodes-DynamoRevit/tree/main/scripts
Enjoy ~
Ali T.