Stuck the Logic Analyzer on a few chips, two 6116's and a LS32. One 6116 doesn't have activity on two I/O pins but the LS32 had a couple of outputs that didn't match their inputs.
Pulled the LS32 and plugged it into the tester, bad IC, gate 3 & gate 4 errors.
Since this is the first confirmed bad component, I'll start there and hopefully the graphics will be good and not something else down the line has failed as well.
Oh yeah, why did I choose those chips to test? They were in the immediate vicinity of the A01 ROM chip, which I isolated earlier as the foreground graphics ROM.
Now if only I had a stash of LS32's... The anticipation waiting for stuff is bad enough. Waiting for parts is just cruel...