500hp 408 with Hi-Po 340 Manifolds?

It would be much easier to make the power - but you then have to pump it through those manifolds... That's the problem. Then head work is critical regardless of the head design used, and the camshaft will be just as critical because the exhaust will only be working against you. If you think about it as having to make 550hp with headers in order to make 500 with manifolds, you'd be thinking in the right direction.
The FAST guys will not be easy to get info from. For a camshaft once the head package is known (and I don't think RHS are the way to go - you need more head) give Dwayne Porter at Porter Racing Heads in VT a call. He does some amazing head work and camshaft development for the FAST guys.
Jake - your problem is the column shift - but you knew that.