This afternoon I finally bit the bullet and took the crank web clamps off the WW1 ABC crank, pulled the rollers out and fitted it into the crankcase. Yes, that's right, you cannot get the assembled crank into the case. It was difficult even then and I had to use a screwdriver as a lever to prise a bit of give into it so the rods popped out into the boreholes.
Mad way of going about things, but of course it does make for a small, stiff box & it's why they'll run up to 8,000rpm without exploding!
Refitting the rollers required a magnetised screwdriver, some grease & about twenty minutes per rod eye. Fiddly but not as bad as I'd expected.
Main bearings next - got them soaking in petrol overnight.