And the real surprise: domed TRW L2394N pistons. That explains the 230 psi compression test results and the detonation on anything less than racing fuel. So what do we have: 10.5 to 1 ratio with the 111cc 7F6 heads?
In googling the part number I found this:
"L2394NF .030 TRW pistons for Pontiac 455, )
.476 dome aluminum forged for high compression.
Unmachined Compression Ratios:
89cc = 12.54:1
96cc = 11.83:1
111cc = 10.25:1
114cc = 9.98:1
These pistons are generally used for racing applications, and may require
machining for proper fit and clearance of smaller chamber heads."