It appears that my services have been requested.
Here are my initial results:
According to the file list for the CMHQ “55” block files, the amphibian vehicles are in the 55/1350 series:
https://heritage.canadiana.ca/view/o..._reel_c5770/19
Unfortunately, it appears that the 55/1350 series files should be on microfilm C-5783 which is not available online.
I stumbled across this very interesting document which gives details on Canadian vehicles assembled in the UK, and claims to list all local contracts for vehicle bodies and modification kits. It does not mention any amphibious vehicles:
https://heritage.canadiana.ca/view/o...eel_c5781/4514
Please note, ATDB normally stands for Army Technical Development Board, which was succeeded by DVD (Directorate of Vehicle Development) late in the war.
I’ll attempt some more research later.