The best stock heads on my kids 87 305 Camaro were the ones off my 86 305 powered 1/2 ton truck. They were 58cc chambers, 1.84/1.50 valves and we port matched and did quite a bit of valve bowl and port smoothing work and with the 87 short block he ended up with 194-199 psi cranking compression. At which point running 92 ron fuel you could only have 32 total ign timing, and the computer(Weird hybrid half vacumn, half computor with knock sensor) kept pulling the timing back to 28 or so and you lost more than you gained.He ran 10 gal 110 octane race fuel, set the timing at 36 degree total and that really made a difference in power, but in the end 58cc heads and flatop pistons w/4valve reliefs on pump gas didn't work, 9-1 cast iron, 10-1 aluminum are about the limit on pump gas IMO