hit up ka-t.org for alot of the good answers. tuning will let u run up to 400 on stock internals, pending the condition of the motor and age.

for most, 14-15psi is max on stock internals, or 330-350whp. from there longevity is risked to a point.

internals are found at lots of shops, AMS, ka24de.com, enjuku, etc. just look for sponsors and searches and they'll sometimes have where they got them.