Racer, the 351 heads work nice ported, but will never outflow out of the box aftermarket heads. Still ,if you're on a budget they're not bad. I'd recommend World Products iron heads. They're between $750-800. They'll outflow 69 castings easily. However, $20 is a lot cheaper than $800. That being said, if you still use the 351 heads use a 302 manifold. I say get the World Products iron heads, solid lifter cam, and a victor Jr. intake with a 750 double pumper, and rev that sucker to 7000RPM's. That's what I do to mine and it traps 107mph at 3000ft elevation.
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92 GT, 4:10 gears, centerforce clutch, 6# powerdyne blower, bbk h-pipe, flowmasters