Help me win this argument 400 in a 72.

400 can't be built streetable? I think he was only saying that putting in a stock stroke 383 or 400 isn't a fruitless or lacking pursuit...

Perhaps, but he used a "12:1 400 running on race gas" as the comparasin.

EDIT: I'm still for a big block, but the rest of the car needs to be put together to accommodate.

Yes indeed. Frame connectors, 8 3/4 or equivelent, I'd almost have to through offset hangers in there too. You are going to need some tires with any performacne build.