When I was a kid I loved baling hay with Dad's VAC and 50T IH baler with the continental engine and a single dolly wheel. Depending on the size of windrow, put it in 2nd gear and set the friction throttle at idle and use the "foot feed" to speed through a thin spot and let completly off in a heavy spot or even clutch if necessary. A live pto tractor and baler cant keep up with a foot feed vac and the engine baler of equal model.
I looked for a couple years trying to find an engine drive baler for my current vac to no avail. There used to be a lot of them when this county was covered up with small daries. Finaly found a NH 65 pto baler and a NH retired Mechanic and I went through it and I am amazed at how well the vac handles it. Seldom ever opens the govenor. I make about 2,000 12" x 16" x 32" bales a year and usualy pack in about 40# of hay if I tighten her down about all she wants.I have about 150 acres of hay ground that I cover twice a year so I roll the most of it.
excuse my rambling.