Well I'm well impressed.
Must have built the bike around the engine and gearbox unit.
How any access to the timing cover is obtained does not look easy, but I have to admire the clever sandwich plate for that front engine mount.. also the adaptor plate between engine and box.
Shows attention to detail, finely executed, and on the subject of a recent topic, the breather arrangement takes a starring role....
Well done.
Swarfy.
Additional...The non standard rear drive gear may be a bit more rugged than BSA's original worm gear.