If you are talking about changing the transmission with the engine in the truck (which I assume you are) it should be a relatively easy job if you know what you are doing. I just did this recently and it took me several days of fighting to get the newly rebuilt transmission back in. What the shop manual does not tell you is that you need to removed the cross member at the rear of the transmission on order to get the rear support for the transmission installed. Its also a good idea to use the alignment pins or dowels described in the shop manual as you are removing the transmission to keep from putting excessive pressure on the pressure plate and causing it to become mis-aligned with the clutch and not allowing the front of the transmission to go back in and engage the crank shaft which will require you to re-align the clutch. Don't ask me how I know.
If you are changing out the clutch I am pretty sure the bell housing will have to be removed. This I did not have to do in my situation. Removing the bell housing would require supporting the rear of the engine, removing the rear engine supports and then removing the bolts holding holding the bell housing.
Mike
