I had an MX4800 with a loader. I always used 2 chains, both grade 70 5/16, with 5/16 ratchet binders, or occasionally the cam-lock binders. I'd remove the draw bar from the tractor and run on chain through the draw-bar hitch and then at an angle on each side to tie downs further back. On the front, I use the bumper / brush guard / weight bar area; run a chain across or through that, going forward at an angle on both sides and hooking in to tie down points ahead of the tractor. I never use four chains...its more inconvenient and I find if one gets loose, they all do.
It is worth putting the tractor into 4x4, the lowest gear, and applying the parking brake.