Eventually found a single page spec sheet that was packed between layers of foam packing. It says use 15cc crankcase oil. That’s just about the sump volume as it appears to the eye. It’s a generous splash oiled sump, heavily constructed out of cast brass, which will help cool it, given sufficient oil volume.
I hear from at least one other who cannot get the oil cap off. I suspect, based on the flow of my correspondence with the vendor, the maker didn’t realize they had a problem, because they install the oil cap before the intake manifold is installed, and they weren’t aware of the issue. I’ve fixed mine by re-profiling the cap to a truncated cone with a straight screw slot. It works.
But the short run didn’t really hurt it. Scored the piston on the bottom side, as well as oil charring on a pushrod, sticking the valve open, and bringing the show to a halt. Dressed the piston with a fine, flat file and a bit of 600, and changed the ring. Did the other side while I was at it.
This is my first time assembling a boxer engine. At this scale, lifters and cam bearings and rocker hardware gets crazy small. Working through the gear case opening and assembling the jugs and rockers and whatnot on a 1.6cc cylinder gets interesting.
I get the added fun of a short window of visual acuity each day, after which the blur and haze eliminates too much detail, even with magnification. Stuff simply takes a bunch longer. Drop a C-clip only about 3 mm overall diameter, good luck finding it, etc.
I note the domed piston and hemi heads.