Well, you need a plan. Are you going to put it back to how it was from Jeep, or replace all the wiring? You going to hack it until it's driveable, or fix it all nice and reliable? There are several companies that make aftermarket "hot rod" harnesses that give you the wire and circuit. They expect you to route the wiring and terminate the wires for the various devices. The main advantage is lots new wire in many colors, which would be expensive purchased by themselves. Search for "painless" on this forum and IFSJA.
The original wiring does not have a fuse panel. Instead it uses a circuit breaker in the headlight switch and strategically placed inline fuses in the harness. The hot rod harness will have a fuse panel, which would be an upgrade.
'73 was the first year for the GM column, and you can get a harness that is meant for that column. Might be a good place to start since you already have an engine swap. That'll put back the key starter switch that locks the column, if you repair anything that's broken in the column.
A new replacement harness specifically for that truck does not exist. You can fix what you have and adapt it to the Chevy, if that's what you choose.
Do you have the '73 TSM? That contains the factory wiring diagram for '73. The diagram is also here
https://oljeep.com/gw/elec/GW_wiring.html though the quality of the transfer is likely better if you get the actual TSM. Plus it will include info about the rest of the electrical system. I would suggest you copy the diagram double sized and get some colored pencils to follow the wires.
Basically it comes down to laying the circuits out on paper (however you do that) and going one circuit at a time until it's sorted. Multimeter, test light, whatever splices you prefer (solder, butt connectors, crimp connectors, crimper ... lots of opinions and variations here), some extra wire, test leads, etc. Get a good book on automotive wiring, or study some online if you need to improve your understanding of electricity.