Wait, a Sun machine? Your neighbor just casually has an old Sun diagnostic machine sitting in his garage in Akron? Those things are like the holy grail for old school tune ups and most of them got scrapped or rotted away decades ago. The fact that he walked that thing across the street and had your Chevelle running right in 15 minutes is wild to me. Six hours with the Harbor Freight light vs 15 minutes on real equipment tells you everything about why those cheap ones are basically a paperweight with a cord. Chasing a misfire for 3 evenings over 2 degrees of dwell would've had me pulling my hair out.

How did you figure out the oven was running hot, did you test it with a thermometer or just guess after the cornbread failed? I'm curious because mine browns stuff way too fast on top and I've never bothered checking.