head casting number 4772576?

mguner,
I wouldn't use either of them as they would be too much head for the 318 and exhaust manifolds. As for the 915's and the magnums the magnums will flow better, but in both cases they are too large for the little bore of the 318. And with the large ports and the exhaust manifolds the bottom end (low RPM's) will suffer IMO. I would use 360 manifolds on the 318 with 318 heads with some work done to them. Then you should have a fairly strong running engine and have some fuel mileage too. What I do is bowl blend the intake side and gasket match the intake side, and keep the stock size valve, and do a good valve job, and stop at that. Then on the exhaust side I would use the 1.60 from the 915 and use a 75* cutter and do a good valve job and your done with the heads. As for the short block we used the 85-90 pistons for the 318 as they were .020 taller compression height and used all standard parts ( rings, and rods), with these mods you should be between 280 and 300 HP to the rear wheels and around 350 or a bit more out of the engine.