An old Quadrajet is good option if you can find a decent one. Only problem is the spread bore, if you have an intake with spread bore great. If square bore than Edlebrock or Holly make good crabs. I'd be looking at the 750 cfm range for a 454, vacuum secondaries based on how you plan to use it. You will spin it past 4000 rpm, at least 4500. If you don't then you should have put in a 4 cylinder.
Seriously, it's hard not to spin past 4000.