if the motor runs and works fine now and you just want 140-150 just leave the motor stock. Even the weaker blacktop n/a motors should be fine at that power level. Just get a good turbo, 11mm GU pump, water meth injection, cooler , exhaust, intake manifold lift and good tune and ull be fine. I seen some youtube vids of a blokes n/a blacktop motor with 30psi through it and 500,000km and it was fine. You wont need that much boost to make that power and with low egts I think ull be ok.