Warm up the engine by driving 15 miles, shut down and block the throttle wide open. Disable the ignition and recheck compression.
All 8 at 145, cold, is pretty good. Warm, if you check compression and several cylinders are not within 10% of the others, dribble in a half teaspoon of engine oil into each cylinder and roll the engine over several revolutions. If compression rises materially, worn rings. If it stays the same, worn valve seats.
FWIW, one of my Olds 455 marine engines will show 150 - 160 psi, hot, with a compression ratio of 9.7:1. (We build them to run on 87)