As with any car, pay attention to what you're doing, and be very organized, at least with all of your bolts and fasteners. Since I've never done heads on a SHO, I can't give you many specifics. But yes, timing belt needs to come off, as well as intake and valve covers. I see no reason why the exhaust manifolds could not be left on the heads to pull them, but the y-pipe must of course be unbolted. If at all possible(again, not too familiar with SHO head gasket replacement), try to leave the cams/caps, and the chain and tensioner in place, as it will save you alot of trouble setting the timing again.
If you haven't done it, while you have it torn down, be sure and do your 60k, along with any accessible oil seals, water pump, and T-stat. What better excuse?