Firstly you need to be sure the numbers are original or there is very little point in researching any history.
Assuming they are WM20 76321 doesn't appear to be in the post war key cards or the Australian Ledgers which would have been a possible route to the Pacific.
WM20 96045 is in the post war key cards, this machine would have been the donor for your engine during a rebuild, unfortunately the last known place on the card has been scratched out and isn't discernible from the scan but it may be possible to recover it from the original document held by Lex? (card 212B)
