When I was in Florida in January there was a man making things out of alligator hide - he was using a monster Singer 15 with a walking foot - he had it on a treadle and he had welded an auger handle to the wheel so he could tread or hand crank or do both. Those gator hides are THICK. The 15 he had was large but it took regular bobbins.
I'm guessing if you get that machine working a hand crank would quilt saddles if you wanted. You might want the option of treadle AND hand crank to give you a little more leverage. Those old industrial machines turn very easily so it might not be that much of a chore to hand crank unless you really do quilt those saddles.