Well, the results are sobering.

compression as follows in psi:
220 240 190 240 250

And take a look at this coke buildup on the crush washer and injector of piston three (the one with low compression). Perhaps this crud broke off and scored the walls/rings? Part of me was hoping the damn thing'd fire up once I unblocked the crush washers...

The engine was definitely worn before I ever got it running on wvo (previous compression numbers are pre-conversion), and it had some repeated trouble starting this winter, even with the block heater. Alas, it appears I'm just another ignorant human mistreating a machine.