Final dyno numbers for my 1965 tripower 421HO was 430 HP and 485 Ft-Lbs Torque. I installed the motor into my 1965 GTO which is equipped with a Muncie M20 4spd and a 12-bolt posi rear-end. The exhaust runs through a set of '67 HO exhaust manifolds and a 2.5-inch Pypes stainless steel exhaust system with electronic cut-outs.
Check out the personalized California legacy license plates ("1BP 421"). Butler built 421!
B.P. built Frank a stock appearing 421 but made it pump gas friendly and upgraded with a mild hydraulic roller cam. He sent us some info and pics once he finished putting his Goat back together. Great job Frank!