If you go peruse this thread by BentwheelBob (who now owns and restored my black 455HO Formula) you can see what he did. He built a 461 stroker with 474hp/550 torque off the original 400 engine in his 78 T/A. Bob is a great guy and quite entertaining to read. And he had a set of modified 6X heads built for the project (similar to the heads that I used on my 455, from the original 350)
http://forums.maxperformanceinc.com/...d.php?t=755425
engine info here:
http://forums.maxperformanceinc.com/...d.php?t=755425
http://forums.maxperformanceinc.com/...755425&page=18
dyno results
http://forums.maxperformanceinc.com/...755425&page=39