ERIC -I've never had a Quiet Line tractor but from looking at parts books & service manuals and knowing IHC like I do I bet everything on the tractor interchanges from a 1250 to 1650. I think there were some option differences, like maybe frt and rr tire sizes, hyd. lift was std on 1650 but an option on 1250. Only engine parts should differ, the 1650 will have a different but interchangable block, head, carb, etc. than the 1250. The 16 HP Kohler has ten head bolts or studs, and the 12 HP like the 10 & 14 HP only has nine. But even with the big blower housing & flywheel the 12 & 16 Hp both bolt up the same in either tractor. And all the bolt-on stuff attaches the same to either engine like the carb, starter, PTO clutch, etc.