Don't write off a stroker just because you want to keep your manifolds. Just need to pick the right cam for the application. Displacement is your friend.
I would do the 400 stroked to 496. CNC Stealths with dished flat tops zero decked for 9:1. With a cam ground with HP manifolds in mind (see Dwayne Porter or AndyF) you should knock hard on 500hp/600ft/lbs and be all done by 5000 RPM. Nice street engine and only needs 87 regular gas to boot.
