Stock for Stock here's a best to worst list of the BBB heads.
1 67-68 400 & 430 big port heads
2 400 & 430 regular heads
3 70-71 and even into early 72 455 heads
4 late 72 to 74 455 heads
and throw the 75 and 76 455 heads in the scrap pile...they're worthless, but the 75 and 76 blocks are the best.
Cranks and rods are the same for all years 400-430-455.
All the heads listed above are close to being the same when you start porting. If you want an aftermarket head that looks stock appearing, get the TA Stage 1 aluminums. They're sweet and they cost about the same as a set of ported irons.