I would imagine if your engine went south, you could (with a few modifications) swap out the engine and transmission with any of the 300 turbo diesel engine/transmission combinations from the late 70's to 84. I have always liked the look of these trucks but as you mentioned they are very underpowered (sloooow). If it is rust free and not to expensive I would say give it a run.
There many informational and parts listings on the web for this vehicle.
http://www.jefflondon.net/InventoryV2.htmexample:
Mark