I believe the gear box is the same, but the steering shaft coming out of it will be longer for the heavier trucks.
Get or make a few new gaskets and get a seal for the sector shaft from any local auto parts house. GM used the same seal for a bunch of years. Add some thin grease and you are good to go.
Do a search for steering box grease or oil or lube, you will get a bunch of information.
Joe
