you might look into getting a new style MF electronic rpm/hr meter for the tractor.
the later model mf used electronic meters and they hooked to the coil on a gas model, not really sure where the hookup was for a diesel.
but my old TO-35 has a generator with the gearbox mounted to the rear, you do not want that thing to go bad on you. They are very expensive.
the main shafts are longer with gears cut into the rear of the shaft, so you cannot convert a reg generator to a gearbox type.
I would much rather have an alternator and the electronic tach, if possible, unless you are reworking a show tractor.
it's worth a look/see before you invest in an old generator with gearbox.
They also made alternators with gearbox on the back but they are even more rare.