The 400 crank requires the main journals to be ground down to 350 specs, not a cheap job. Then there's clearancing the block, and special (not cheap) pistons. Not a job I'd wish on anyone who isn't after lots of power. Stick with stock parts, if it works out, go crazy on the next one!
Badger cast pistons are reasonably priced, and work as long as you don't run them at high RPM for long periods.