Robert,
Agree on Pic 3, only I'd call it an "M" as I think MT was a tricycle front end.
I had a 49M and noticed some differences also:
Tires--Mine didn't go above the height of the fenders, and these look wider also.
3PH--Mine had the original JD "bar lift" (not sure what they called it), where the implements (cultivator, plow, sickle mower, ????) had a C type tube that went over the bar, with a spear type bar that went several feet forward and was lifted by a linkage under the tractor as the 3rd point of lift.
Seat--Think the metal back and side bar were added. Mine had a thin metal backing that might have had a small pad on it.
Front Grill -- mine didn't have one
I thought about putting an aftermarket 3PH on mine, but it had a belt pulley gearbox right where the top link would need to fit on the tractor.
I couldn't believe how well mine would pull! I used the cultivator with sweeps on it to work about 1/2 acres garden. I noticed one evening that the muffler was glowing RED when it was pulling hard......
Ron