Welcome to the board.
Getting a title for your truck will depend on which state you live in. Some states make it easier to get a truck without a title, titled, but others can make it really hard. Maybe the state in which you live has a web site that can explain possible options on getting a title for a truck that doesn't have one.
Usually, you are way ahead if you can find a way to get a copy of the trucks original title.
Hopefully, the people that had possession of the truck for years, can help you get its original title, or at least jump start what every process your state requires to get a title.
I probably would not invest a lot of money into the truck until you figure out how you can title the truck, so you can buy plates, and will be able to drive it once completed.
Once you have a title, or at least have your States required process started, you can install any motor or drive train into the truck you want. Some drive trains are easier to install then others, but all require at least some custom fabrication to get the job done.
There are several build threads on this board. I suggest you look around and check out as many as possible.
I really do suggest you find out what is required to be able to get a title for this truck before you get too far into it. Getting titles is becoming increasing difficult in some states.