For nitrous I don't suggest you run a 1250 until you get to the 580" or bigger range. With a 1250 the throttle moves less to run the same RPM as a 1050, and so it runs on the transition circuit to a higher RPM before the boosters start to flow. You can certainly make one work with custom booster inserts, but until the displacement is larger I don't think you will see any difference, and it will make tuning with a tight converter real sensitive. NA with a lot of converter, no problem.

FWIW my 525 B1 had a 2.100 Throttle blade and made right at 1100hp. CFM wise it was in the 1180cfm range. I prefer three circuit carbs myself as it fits what I do. Some will argue that point and I understand their reasons, bit for me I prefer the third circuit.

PM message waiting for you Al. Thx.