I would skip doing it, as there will be more conversion parts when you go with the 390. Why not go with a 428 though instead of a 390. Same family FE engine, and it will make better power than the 390. You can do well with the 390, but its not a real performance choice for a motor.
Tranns are rated on torque not HP by the way. and they can hold mroe than you think.
SKyler
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-1989 Saleen Mustang #406- TFS Heads, E-303, edelbrock intake,70MM TB, 73mm MAF, off road H, headers and 3chamber flows.
12.55@107mph
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