500 hp 360 ??

crackedback said

That's going to have to be a VERY aggressive hyd flat cam.

6 paks look cool, will likely go backwards, quite a bit, from a similarly sized single 4.

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My first thought.
With a 4" arm in there , no problem getting close.......you could screw up your way to 450.
A hyd. flat tappet would probably be the first thing I changed. Hyd roller or solid f.t.