So many variables, but depending your budget Ventrac ($$) has about the best options. Zero turn can work moving up and down not so great sidehill. I do some with a 60' Toro but will cause a bit of tire scrub of your grass, I just live with it. Bigger zero turn has better center of gravity but...
It sounds like you have an old style Jimmy two stroke, they would run very well backwards. When this happened many had oil bath air filtering and would suck the oil in. Literally the engine under stall conditions would roll backwards and start.