Here is a link to the AMK sight, takes some patience to navigate ?
https://www.amkproducts.com/
There complete catalog is here in PDF files
https://www.amkproducts.com/Catalog_PDF.htm
And the handy GM# to AMK # charts are here. GM starts on pg 408
https://www.amkproducts.com/Catalog_PDF/403-BC.pdf
I have had some luck using Google search by entering the GM# and often a direct link to AMK will pop up. AMK is good, not perfect, some kits are not always 100% and need to be adjusted for correctness. This is where studying unmolested cars can be a big help, and don't get to hung up on any one head marking. GM and Fisher Body had many vendors for like items. Hope this helps ?
Mike