The SCG catalogue lists many R14 variants, mainly due to different input / output pulley arrangements.
Another important difference was a different front mount used for different vehicles, seen in the first image.
There were two variations, seen here side by side:
The part number is cast on the side where they are fixed to the vehicle:
We'll identify the bigger left casting as "a", it is numbered 36475, and the smaller right one as "b", numbered 36127. When swapping gearboxes, it was a straightforward swap of the two brackets if they differed. The SCG catalogue denotes the following brackets were used on the following vehicles:
108s principally had the "a" type, other than 51416-24, 51901-50 & 52037-65, which had the "b" type. This seems to correspond with the movement of the coolant filler from the bodyside to the solebar.