A few things:
1. First and foremost, what is the title situation?
2. If you don't have the title, look what its going to take to get a title in Utah.
a. Is the serial number/vin still there? if not what do you need to get inspected? I see you're a peace officer, can you sign off on your own inspection?
Don't do that much work until you get these sorted out. NO BIG TICKET PURCHASES UNTIL YOU GET THIS SQUARED AWAY
3.Looks like a frame came with the 54. What's its condition? may need to find a good frame or S10 swap...
4. If you find your still serious, buy a shop manual and factory assembly manual
https://www.amazon.com/RESTORERS-CHE...nd+shop+manual
5. Start drafting a build plan that you can schedule, budget and work against.
I hate to say it but that 54 looks like it was in a decent fender bender w/potential roll over...that's going to take a lot of work to get squared away plus there's a lot of slight differences between the 2 cabs (47-53 vs 54-55.1) so its not like all parts are 'plug n play'
Not trying to be debbie downer here but it looks like both cabs and body are going to need ALOT of work, nothing impossible but time. If you dont' want the time then its money for repop parts. It can be daunting...just looking at it day in and day out.
So my advice. Get the title squared away or figure out what its going take,
no big ticket purchases until you get that taken care of. Next, to be honest I'd be on the look out for one more cab. You also will need to start thinking about drivetrain; engine, transmission and rear end. Last figure out what direction you want/need to go w/frame as it is the foundation of your build.
I can't speak for the rest of the folks on the site, but personally i find researching and learning all the nuances from this site, shop manuals and parts catalogs fun almost as fun as wrenching. Also get out to shows if you can and see what other guys have done with their trucks. What do you like and what you don't.
good luck and keep us posted. If this truck doesn't work out, it means it wasn't meant to be and thus you were meant to find the good one
TL/DR:
Get title, figure out frame, Start researching, Start looking for more parts.