OK, I think I have it now.

This model does indeed have the bent tube between the IP and the engine block. Looks sort of like the tube you use to check start of injection timing, but no angled cutoff on the end. It is attached to the IP with a standard banjo fitting, and apparently remains open to atmosphere all the time. (Apparently there are other models that had the remove-it-yourself check plug.)

Not wanting to oil my driveway (again), I cobbled a little sluiceway from aluminum foil to route the anticipated overflow past the back of the IP and into a drain pan. Worked great, except that the vent port apparently isn't very big, and at just over 1/2 quart of new oil, the fill port began overflowing. (So much for good intentions!) I'll let the thing drip for a couple of hours, then put 'er back on the road, hoping that any unsuspecting motorcyclists know enough to avoid my oil trail...

Again, thanks all!