This is a stock 403 short block, correct? Even with a 64cc chamber and Felpro gaskets, you will only be at 9 to 1. I was at 9+ to 1 with the small 204/214 cam, no issues on 91. The #6 heads had 2.07/1.56" valves with the bowls opened. You are using a manual trans 350/442 auto cam, like 217/218 duration? If the rod bearings weren't toast, should have checked them first, supposedly had a tick, assumed lifters or exhaust. I replaced the rod bearings, showing copper and main bearings, looked OK, no more clatter but still shitty oil pressure warm. The crank need turned and new bearings. Shitty with the 1600 stall and 2.78 gears. Easy 1/4 block one wheel peeling with a 2350 stall and better 2.74 first gear.