89 body 92 magnum swap

Hey all, amateur here.

I'll try to make this short and sweet. I have a 92 dodge with the 318 magnum, auto tranny. Came from Michigan so body is about rusted to ****te. Was considering doing a frame-off restore and rebuild but I obtained two more bodies/ 1 engine for 500 bucks so I've decided to do some switching around.

I have an 89 body, no motor with a 4-speed standard and an 85 with the LA318. The 89 is the best body out of all, just missing the grille.

I'm leaning toward swapping in the magnum but I want to hear some second opinions first.

The magnum runs like a dream, it just turned over 200k while in my possession, a little over a year. When I first bought it I put in a new Walmart battery and gave it an oil change, and that's all I've done. I have no information about other work that may have been done, as far as I know it could all be stock.

Started up and ran perfect through winter, got me to work on 4 bald tires. I live in southern Idaho, we had a wild winter last year and they're predicting another for this year. But anyway, it sat for a week this spring while I was moving to a new house, and when I went to start it it was dead. Takes a bit to jump start but runs fine once it does, and as soon as you turn it off it's dead again. So alternator issue or crappy Walmart battery or both.

The LA, I have absolutely no knowledge of. Needs jumped to start as well, but it runs.

My question, I need my rig to be dependable and not leave me stranded come snowfall. So which engine will be my safest bet, and while I have everything apart, what maintenance should I perform that would be a good idea?

The tranny in the 85 has been expose for god knows how long, I seen some surface rust on the front. I went through the gears and had issues putting it in reverse, should I rebuild the tranny while I'm at it?

Personal opinions great, or if you have links that works as well, I'm on my phone and these sites are a chore to use lol.

Thanks

AND also, what would be required for the magnum to work, if I decide to go that route

swapping that 318 magnum into the 89 will likely be the easiest. the 88-93 trucks are all almost identical other than small changes like the engines/trans and wiring. it should all swing right on over. there is a lot of time consuming work but it could probably be done in a couple days if you don't run into any issues. most of the work is in just swapping the wiring harness over.

Sounds like you have a parasitic electrical drain somewhere. My tuck sometimes sits for weeks on end with no ill effects on the battery.
Good luck with your engine swap.

oh ya i forgot about that part. you can test for a parasitic drain easily. disconnect the ground wire and stick a test light between the ground wire and terminal in series. if the light is on at all there is something in the electrical system that is causing a drain. if the light is on just start pulling fuses until the light goes out and then figure out what is on the circuit that is causing the issue.

Thanks for the advice! I've had a couple buddies take a look at it but I haven't gone deep trying to find the problem. I will for sure try this.