Well, today we got the magazine catch cut machined and installed the catch, then made some springs and pins to get the lockwork functioning. Relieved the bolt for the feed ramp and magazine lips, at which point I had to try it out!
Unfortunately, not a semi-auto yet. Feeds ok manually, but tends to smash cartridges every which way when feeding automatically. That is probably on account of the minor modification I did to the feed lips to clearance for the bolt, which seems to allow the rounds to rotate up rather than just going forward. So my options at this point are either make my own magazines that control the cartridge longer, or make substantial mods to the gun, including setting the barrel back, reconfiguring the bolt, and machining to allow magazines to come up 1/4" higher.
The good news is that it fires & extracts just fine. Puzzling, though, is that ejection was 100% at first, but somewhere around 20 rounds in, it started catching empties and smashing them. Now it's doing it more often than not. Not sure what changed, as cartridges still eject very positively with manual bolt operation.