Both the 656 and 544 hydrostatic appear in the IH buyers guide for 1969. I believe other models came later. Specs: Gear drive 656 (gas) - 63.85 PTO and 55.94 drawbar HP Hydrostatic 656 (gas) - 65.80 PTO and 51.88 drawbar HP Gear drive 544 (gas) - 52.84 PTO and 45.51 drawbar HP Hydrostatic 544 (gas) - 55.00 PTO and 42.00 drawbar HP Greg Hass Michigan