I doubt you'll move a ton of air volume through those RHS heads unless you move the pinch over...so with that I'd settle on a 1000HP or the new Ultra 850HP. The new carb has so many great features, this is the carb I would run.

I agree with others though, if you can test a few borrowed carbs AND take the time to tune them at the track (not always possible) then you might be able to make a better educated guess.
I've used the 1000HP on many different engine builds as well as the 950HP and IMO you cannot go wrong with them...just that the new carbs have so many upgrades for around 100.00 more it seems worth it to go that route.
Good luck with it!!
Brian