While not a 57, I'm putting on 2x2 using an Offy manifold on my 56 BA. The only thing you have to concern yourself with is hood clearance when choosing an air cleaner. On mine I'm using a 2 barrel adapter between the carbs and intake. This turns out to be the same height as the stock 1 bbl on the stock intake. since I had put a 2" air cleaner on the original 1 bbl when I first got the car I know I can use a 2" air cleaner on my new set up. The 57 hood may have less clearance than the 56, so you maybe you could build shorter adapters, have someone modify the stock intake so a 2 barrel would bolt right one, use 2 1 barrels on the Offy. The reason I'm only mentioning 2 carbs is because in my case that is the most I can put on and run A/C.
