John,
That is an 82 series mule drive and undercarriage. It will not work on a 107 as-is.
Sorry to say, but the 107 is indeed a narrow frame tractor. I have a 127, and 10 other wideframe and 82 series tractor, Don't be thrown by the rear fenders. The 1x6/7 tractors had a very similar rear fender deck to the following wideframes, but are still indeed a narrow frame tractor. Look at the frame where the back of the engine is, on your tractor, it will be a straight line from the grill to the fender pan. If it were a wideframe, it would actually spread out at the area of the back of the engine and that area, to the grill would be a couple inches wider. When you had that mule drive installed, did the forks even touch the frankenstein bolts on the frame above the axle?
I have never tried to make an "A" or "C" series deck work on a narrowframe, so I am not sure if the right combination can be put together to make it work. One thing that you will run into, is all the pulleys on the narrowframe mule drives are straight. The pulleys on the "A" and "C" series deck are angled toward the carb side rear tire. The center pulley lines up in a different place between the 2 types of decks.....