Found my dads original 1971 duster!

If there are holes in the flange, that is probably where the shroud should go. Being all stock, it should all bolt together without drilling new holes.

I think you are overthinking it.
Ya. I thought so too. But my rad is original rad and has no holes or provisions for attaching shroud. It even stumped the owner of national moparts. He told me that if have to take it to a rad shop to have brackets made up and soldered on or figure out another way. He looked up my rad number and said he had no idea why it didn’t have anything on it to attach shroud