The long block will be the same other than jolt ons like that double roller chain
And on the earlier LA engines having more CR, weren't the chambers in the heads in the earlier ones a bit smaller as well?
I will say this... Quite often if you actually measure things out actual compression comes out less than what was published back in the day. Lots of "8.x :1" advertised motors actually measure out in the 7s :1.