You should be able to block the truck up at the steer axle and gain access to the crank pully from the underside, If your going to this much trouble, you'd be better off in the long run to replace all of them at the same time, 'cause sure as the sun will come up tomarrow, the altenator belt will break next week. Just remove the 4 bolts and slide the coupler shaft twords the Hyd. pump, you'll have to remove the alt. belt to install the new belt anyway.

On forklifts with the pump run off the crankshaft you have no choice but to unbolt the shaft to get the belt on. After removing the 4 bolts it should move out of the way enough to get the belt on. I'm not sure about how much room there is to get at the bolts on your model, maybe have to take the counterweight off.