Well:
-wiped out the bottom of the gearbox case
-cleaned off the mating surfaces
-over-adjusted one of the gearbox levers again (so, another, fortunately short, bit of time searching for the detent ball and spring)
-moved all the movable gears to one side, and then adjusted the gearbox levers to matching positions
-moved the gearbox cover in place, fiddling with the levers a bit to get them all to engage with the gears, then bolted it on
-tested that all the knobs and levers engaged with their gears properly
-installed the drain plug
-screwed on the cover plate and installed gear levers
-removed the fill plug and filled it up (to the sight bubble) with Shell Tellus S2 VX 32, and reinstalled plug
-ran the lathe for a bit to make sure the gears engaged properly and both the power feed and threading screw were driven properly.
Still to do:
-test that the labels for the knobs are oriented correctly, by actually threading (or rather, just barely scraping a rod) and measuring that the TPI matches what the settings say it should be.
Edit: And I found the Shell 32 oil at my local UFA store (here in Edmonton, it's just a gas bar, but it has the oil in the pretty small "store").