425 hp from a 400 with good heads is ....like rolling off a log easy. Roller cam is expensive for such simple combo. No stroker needed for that level of performance.
Given the costs (at least around here) for machine work You might be 2 steps ahead by purchasing a build kit. Crank rods pistons combo! Obviously FORGED pistons (based on your head cc's) get you into the 10:1 range of compression. 4L80E is another $$$$$ good YES but $$$$ a 200r4 or the 700 are good alternatives each with their own pro's n con's..
TIP...don't forget the set screw INSIDE the block at rear of passenger oil galley(after you drill a .032 dia hole in it), and the dip stick tube goes IN from the oil pan....
sucks to have to pull the pan off a beautiful engine because you forgot to put the bottom tube in.