Just bolt in a 4200 with a decent exhaust and your at 300 HP in near stock form. All the parts except motor mounts are around to do the job.
Want more 6 psi on a stock 4200 is 420 ish HP...
Compete engines can be had if you look around for $1000.
Mods after that to install
oil pan + wire harness/retune == $1100