A complete truck swap from non-AC to AC using factory parts may take longer then most expect.

The heater box and all the heater controls have to be swapped. You have to add the AC duct work to the dash, or it needs to be changed as well. The AC compressor and the associated belt drive system needs to the changed. You need to add the AC condenser out in front of the radiator, and that may also require a larger radiator. The most likely fan and its shroud can be added with the drive belt assembly part of the operation with minimal extra time. Then there are the AC hoses and their needed components (expansion valve and receiver/dryer) that the hoses require be add to the arrangement. Back in the early 70s when shop rates were in the $30/hour range, adding AC where it was not before had a $500-$600 labor bill + the parts and components needed.

If the truck is a project that is still pretty much a pile of pieces, then its pretty much putting the AC pieces in place of the non-AC pieces, and the labor time doesn't add up to much.

If a hang on unit is available, it might be a less effort and less cost option, unless you have a donor truck with a functioning AC system.