Neither one. I would spend the time/funds to obtain a 1976-1979 Pontiac q-jet. Couple of reasons for this. They are large cfm, correct intlet location, linkage, type of choke, vacuum fittings, large front vent for the shaker base.
They are also the later design with APT, and large cfm.
I use a 1977 Pontiac q-jet on my own engine, 455 making just under 600hp. The part number is 17057274. To date it has outran, dyno and at the track, every aftermarket carburetor we've tested it against. Beat them in fuel economay testing as well.
The later Pontiac cores are still quite common, and can be purchased for reasonable prices.....Cliff