Which intake manifold

They probably work really well. Although they are a spread bore, they ain't spread "very far". lol It'd be good on a slant 6.
they surprisingly do!

I had a rolling test lab 69 cuda for quite some time and I'd screw around with different intake and carb combos on the tired *** stock 318-2 that was in it.

the 6904MB is a 450 and has mechanical secondaries which played nice with a old school performer. nice throttle response and drivability.

like you I have one holding down the shop floor too...