What is creating this noise in my 403

Help with my “noisy” 403….

I have a 403 motor that “pings” like crazy… at least I think it is pinging..

I inherited the motor, it had not run in many years. I don’t know who built it and with what..??

The motor runs solid, feels good, nice and cool etc… no leaks, no smoke, no fluid usage, no fluid mixing. Compression test results in about 165-170 PSIG across all 8 cylinders. The valves have proper preload (about ¾-1 turn per pivot bolt)… timing chain is fine … 4 degrees total slop… TDC is right on notch on balancer…

I have severe ping (or a general clanging sound in the exhaust, not on the motor) in the exhaust under light-moderate engine load… at idle or WOT doesn’t sound unusual at all…

The exhaust consists of 1.75” tube headers with flow master mufflers

I have re-cammed the distributor. Tried every combination of vacuum advance and mechanical advance. I have fuel injection on the motor, and have tried several different fuel-air ratios and nothing seems to improve the situation….

I’m running 16 degrees of initial advance, 35 Total Mechanical (in by 2800 RPM) and 10 Vacuum… have tried the vacuum on both ported and manifold sources… no difference..!!!

If I back the initial timing off to 10 degrees it will make this “pinging-clanging” noise at idle…

I have tried high octane fuel with octane additives, etc…. no improvement..

Ideas..??