Swapping Motors

[JCS 0]

Neighbor guy has two SOVERIGNS (1) B&S 16 h.p BAD bevel box, electric lift, old style VICKERS? transmission. (2) Two cylinder motor with a hole thru the block, electric lift, good bevel gear box, good New style transmission. The question: Can he take the B&S 16 hp one cylinder motor and install in new SOVERIGN?? I measured the mounting bolt holes and they are 6 1/2 inches and I guess the CHOLE & THROTTLE cables would need to be swapped from the 16 hp donor also. Any other items??? Will the driveshafts need swapped??? Are they differernt lenghts??