Johnny, you do type a lot of words before you get to the actual question!
The simple answer (as far as that's ever possible with a Bf 109) is that there was a special designation: a Bf 109 G-6/U4, G-14/U4 or G10/U4 carried a 3 cm MK 108 instead of the 2 cm MG 151.
U stands for «Umrüst-Bausatz» or re-equipment set and denotes an equipment change built in at factory level.
Incidentally, there wasn't much point in putting an MK 108 in a G-8 since it was a dedicated reconnaissance model. If the armament was altered on that machine, it was to reduce it (commonly to a singe MG 151 and no machine guns).
There's plenty of material on
Tony Williams' site (and in his books) that you'd probably find helpful.