My dad still has a 730 Diesel. Still get asked now and then if it's for sale, it's not. It's a wide front, row crop with the gas cranking engine.
I can see what you mean, when it's idling you can visibly watch the front tires bounce with every stroke. I have not spent many hours on it but can see how the putt-putt could be fatiguing, especially the bigger diesel models. It does have live PTO/hydraulics, power steering, and a decent suspension seat, really not a bad tractor to run in that regard.
The connecting rods are about as big as your forearms, pistons are like coffee cans. I read somewhere that JD discontinued the 2 cyl not because it was antiquated or inefficient, but with tractors needing more and more horsepower, the parts were simply getting too large for a farmer to handle. The flywheel on that 730 is probably 150lbs.
I was very young when he was using it regularly and don't really remember it that well, and the crankshaft broke around that time so it was parked for a good while. From what he's told me, it was his main "big" tractor for a long time, and even had a loader fitted at one time. Talk about busy hands with the hand clutch.