1962 Chrysler 300 engine Swap questions!

Hey guys its been a while. I recently got my hands on a really straight old 62 Chrysler 300 and its missing the origonal 383/413 haven't been able to figure out which engine was in it yet still trying to decode the body tag, it still has the big block pushbutton trans in it and want to keep it big block. Well I have found a 400 out of a 77 D300 that I can get for dirt cheap and I was wondering if there are any differences in the engine mount ears or major block differences between the early motors and the later motors that would cause problems with the swap? I'll admit I'm a Ford guy and Mostly mess with Y-blocks and FE stuff but I'm not gona pass up a clean mopar and just need some education on the subject from folks that know the RB engines better than me
Author: Kadassa