Maximum advance curve on my 360

My two cents say that your distributor is not advancing accurately every time. It may be showing one thing and doing another. The chances of 2 separate engines doing the same thing are pretty slim. You did use the same distributor for both right? Moper also has a good point regarding cam/converter choice drawing engine down. IMO you should spring for the MSD billet distributor and rule that out first. I run this on my street car 9.8-1 with distributor locked out at 34* total, with 4 speed trans it has never pinged on 92 octane even while heavy loading in 3rd or 4th gear.