The 307 that is original to our 1969 GMC had 185 heads, which are 1.72I and 1.5E
I haven't seen a big valve 307 myself.
Quote:
The 307 used one of three cylinder heads -- casting numbers 3927185, 3986338 and 3998991. Casting numbers 3927185 an 3986338 are early low-rpm torque makers with 70-cc combustion chambers, 1.72-inch intake and 1.5-inch exhaust valves. Chevrolet used the 3998991 from 1970 to 1976, and it was identical to the other heads except for its larger 74.56-cc combustion chamber.
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