I had a similar issue with the Tip-in found in the Holley carbs. I went with several custom carbs and ended up with a DiVinci Performance Carb. Dan DaVinci (Smith) is the guy who made the carb for OCCs fireman's chopper. He just so happens to be about a mile from me in Houston. He made the carb and it was a bolt on and go. I am waiting for the weather to cool a bit before I put my SPF and 402 on the dyno. I plan to reinstall each carb and get the results. But I am very pleased with the job DiVinci did, my guess is 20 to 30 HP increase.
http://www.davinciperformance.com/