As mentioned earlier, the few pre-war and all WD Flying Flea production used a lighter crankcase casting than post-war civilian production despite looking externally identical....

Both castings (L and R) are affected by the differences are more noticeable on the left casing (shown below)...........

During 1943 Royal Enfield redesigned the crankshaft assembly, beefing it up to take 1/2" rollers in the big-end rather than the smaller 21/64" rollers used in pre-war and WD versions.......this affected the conrod, crankpin and crankshafts and as such are NOT interchangeable with the earlier version.........the crankcases too were strengthened by adding more metal and reducing the previous "web" internal design...........although drawn-up in 1943, and approved in late-1944, the redesigned crankshaft assembly and cases did not appear until true civilian production commenced post-war...........

Shown below......top the early pre-war and WD left-hand crankcase portion and below (with bits of orange gasket cement remaining) the redesigned post-war civvy case.....