I would thinik a 60" rotary cutter and a 72" finish mower would be equipment your machine could handle. Obviously, the finish mower is going to be the best way to go for your lawn. I'm not sure exactly what you mean when you say you "want to top a small pasture" but if it's truly pasture with just grass you want to level out a bit at a higher level you could probably use a finish mower raised to whatever level you want. It's not ideal, but you're looking for a compromise... /forums/images/graemlins/smile.gif
Another compromise I've heard of people using is to use a rotary cutter with sharpened blades to do finish mowing. Again, not ideal, but workable. If you're going to do that I might suggest buying an extra set of blades so you'll have sharp, angle edged blades for you lawn and squared edge blades for your pasture.
Good luck with whatever you decide. I hope this helps. /forums/images/graemlins/smile.gif