Wiring will change..... quite a bit actually.
The PTO should line up, but dunno. I think it would be easier to find another engine that do what your getting ready to do. Just my
FWIW, engines up to a 12hp will fit with no frame mods. But the gear drive starter models have big flywheel covers on them. I think, (but not sure) that they were all the same size up to the 16hp. Might have to notch the frame a lot to make things work...... Your tractor, so your choice. I'd look for a belt drive starter motor.