You don't have enough motor for that big a carb, you can jet down to lean it but the bores are big enough that the air will be lazy going thru the carb and that will make for a poor fuel signal. You'd be happier with a 750dp and the motor would be more responsive. Don't worry about the power valve, modern carbs have a check valve so if the motor backfires thru the carb it won't waste the power valve. Trying to get that thing tuned proper will drive you nuts, you'll learn a lot and be good experience but it'll be frustrating. As an example, the high HP hemi crate motor comes with a 750 double pumper, a big cam and tall single plane intake.