[jim sewell]

I believe the answer may lay in these diagrams from W.A.Greggs book , Canada's Fighting Vehicles .

It appears that the standard 12 feet body could have the spare tyre on the outside ( between body and the cab ) or the spare tyre mounted within the body or maybe have run flats and no spare ( although I have not seen 20 inch runflats ).

The Australian machinery bodies were 14 ft and the spare tyre was mounted on the right hand side of the body and have the extended chassis .

The extensions may have been done during manufacture as they are professionally carried out .

Jim S.