We did the same as every other army
When machines came in for major service it was swap the engine / gearbox then back out ASAP
When they sold off the WDB40's about 1/4 of them had mismatched engine & frame numbers which became a problem latter on when we tried to get them registered
Some where I have a copy of the order for B40s.
Went some thing like
495 bikes ( 500 including the 5 test bikes ) + 40 engines + 20 complete frames + 20 complete front ends
The rest of the spares never made it as they got sunk in the Suez canal