If you can get the truck for dirt cheap, then maybe it could be worth the hassle, but the problem is that if it's missing the engine, it will probably be difficult to find a replacement. Even if you do, then you have to find someone who knows enough about the truck to do the work. In addition, with a vehicle this old, you probably have a number of other, smaller mechanical issues, each of which would have to be addressed before being street legal. And finally, you would likely have a lot of cosmetic work to strip away the rust, and improve the overall appearance of the truck. If you have money to burn, then go for it, but it's just not that practical.