When I had my 421, I was running 12 paddle Haulers or 10 paddle extremes. Anything more than that, it would bog off the line.
For carbs, I was running 38 Keihins.
After some major porting and other goodies, I dynoed at 104hp and 57 torque.
For some sweet swingers, call Longhill Motorsport: 503-640-9922. The owner, Dan, makes his own swingers of all types. His welding is out of the world. He actually makes swingers for a major distributors that I cannot disclose.
PM me if you need more info. Good luck!