The major difference in the GT 40 P heads are the bigger valves and revised spark plug angles. It has nothing to do with "side by side what ever BS he was feeding you" Your 351w heads will be the exact same flow as any 302 head after 1973(ish) production date and you will gain nothing. Your GT40p heads will run on 87 octane just fine. Standard valve sizes are 1.78 intake and 1.46 exhaust, your gt40p heads have a 1.84 intake and 1.46 exhaust. People have put regular headers on gt40p heads, but they need to dent them further to have room for the spark plug. A set of shorties that can be bolted to the gt40p heads are about 150 and I believe are made by MAC.
The gt40p heads are nice heads if you gasket match the ports, and smooth out the runners and combustion chamber. They are good to .500" lift on your intake and exhaust cycles with standard valve springs and rockers.
And your 10.5 : 1 compression ratio is still within tolerance to run regular unleaded fuel.
Last edited by Never_Evil; May 15th, 2009 at 02:50 PM.