1968 B44 trials hybrid bike. Likely engine bought as a spare. Primary cover marked 40-1003 in casting. No inspection cover, no drain plug. Possible that screw under alternator can be a level screw. Drilling inside cover suggests that. Different than the covers on my B40WD and my Victor Specials.
Anybody able to confirm if my guess is correct about the level screw?
It's a C15 primary chaincover, also fitted to B40 road bikes. Have a look at the screw bosses inside it, one will have a small hole drilled though the side of it to where the screw passes through - that's the oil level screw - another will have a cutaway to the screwhole by the jointface - that's the drain screw.
Exactly as you described it. Thanks.