After doing some research in various catalogues and looking on the internet at the US Radiator site, I am very confident that ALL big block Camaros should have a radiator with a core that measures 23" wide from tank-to-tank. The small blocks with very few exceptions (Z-28s?) look like they came with radiators with a 21" wide core. Someone correct me, but I believe a 2 row, 3 row and 4 row all have a different thickness, but are still either 21" or 23" wide. Having said that, my '67 has two sets of holes punched from the factory on the drivers side of the radiator support to accomodate either the 21" or 23" wide radiator. So it appears that if someone wanted to get more cooling from a 23" radiator, it would be a bolt-in replacement for the 21".
Anyway, when ordering a fan shroud, measure the radiator core from tank-to-tank and give that measurement to your parts guy so he gets you the one that fits. I put my fan shroud on the new 23" radiator last night and it fits perfectly with no cutting required.