Now I know why army is wanting one to build ! 😂😂It's a better engine/block than a 428-455. Much stronger mains and better integrity. The only Pontiac block that is stronger is the '59-'63 389 block.
You basically have the best 400 block Pontiac made....best iron, highest nickel content, best casting, and best machining. (1967--74 blocks)
The big journal 421-428-455 blocks have rear main seal issues and crank journal/main saddle issues at RPM.
I would much rather run a 400 or a stroked 400 block. I've been driving these cars for the past 45-ish years steadily. YMMV.