The Drive side case is from a Model 7 500CC engine. The Stamping G12 and engine number 44887 would suggest this as being from a dynamo model as manufactutured in 1952. See attachment. The Timing side case is from a later non-dynamo engine. Probably from an alternator Model 88 or 99 manufactured 7 to 9 years later. It would be quite difficult to build this engine into a 750cc motor as that would require extensive modifications.
The Norton factory always stamped both cases and sometimes the Timing Cover with the same number. On the Drive case this would be inside just above the bearing. On the Timing case it is outside usually just above the half timing pinion shaft.
AJS/Matchless Crankcase used 750 cc Norton Type