Getting to 250rwkw in N/A form I would think you'd need
stroker (347)head work maybe even some good aftermarket heads
Definately a cam change
Inlet manifold
Or bolt up a supercharger and your there with no hassles at all.
Grunter made 270ishrwkw running 10psi though a stock 200spec motor with exhaust and extractors.
Which ever way you go bring your wallet cause its not going to be cheap
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