If that piston picture is after the "Cut down the forged pistons to reduce compression" I'd bet the original was more than 9:1. Depending on the 302 year, stock CR was 7.5:1 or less. That's a big "lump" on the piston.
Interesting that the gasket was blown out between cyls 1-2, 3-4 and 5-6 and NOT where the extra water passages are between 2-3 and 4-5.
Stock distributor advance is 24-28 degrees at 3200 rpm. 50 degrees is way too much.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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