This will be a real enjoyable project.
I agree with Woody, Cletis, and George. Why "upgrade" anything? The value to this truck would be that it is a very rare "original".
The original drive-train (and mildly "modified" existing drive-train) would be very easy to maintain and would be very well-suited for non-highway driving (these trucks were not meant for highway driving - an open cab and they drove through the neighborhoods at low speeds.
How much will it cost to buy?
How much sheet-metal rust is there (check the lower inner and outer cowls and all around the floorboard)?
Do you have mechanical experience (brakes and front-end parts)?
Can you weld sheet-metal?
Have you ever painted a vehicle?
