Well, "whichever" you choose, I would stay in the 600 CFM range. I don't think you will be disappointed. Even if you choose the 1406 and it's a little lean you can always make changes. The one I had was on the stock 351M in my 75 F250. It's a pretty heavy truck with a larger engine and it did pop badly when cold and even sometimes when warm. I went up 3 jet and metering rod sizes and it ran great. Now I have a 625 Street Demon.....one of the little three barrel carburetors. It runs very good with that.
