71 valiant engine build, which carb to use

You already own the best carb for that build. 650 AVS2.
We dont yet have a 650 avs2, we have a 600cfm and an 800cfm, we would have to buy the 650cfm. Which is not a problem, at this point there's so much money into it that buying a new carb that will work right for the build is just a drop in the bucket. That said, if one of the carbs we have would be a good choice that would be great.