Dirk,
Read a article about few months ago about a junk-yard 4.6. They put a turbo on it & it dyno'd over 600HP w/ stock internals. Injectors were a concern; so those were changed along with a few other provisions. budget was less than 2500.00 for everything. With considerable boost, it held up good. Totally stock motor from junk yard Mustang.
I am not an expert, but on this motor w/nitrous it is more about fuel & timing at this point. Without proper support in the timing & fuel delivery department, it will kill itself eventually. I would think people would want to know what ign system (MSD/7ALetc...) & what fuel system (what carb/injection, jets, pump, reg, etc...) before taking a stab at that question. Scoot