I haven't been on here in a long time, but decided to take a look this morning and saw this thread. Good to see someone else with an appreciation for these first gen trucks.
The wiring diagram you offer to post would be a very handy thing since the negative-switching ground has given lots of folks issues in the past. I haven't ever done LED headlights, but every other exterior bulb I can touch , I like to switch out. Ballast resistors are necessary to keep the turn signals functioning correctly, and as a tip, I've found that adding one per side, but only on the front still works to avoid hyperflashing but speeds up the flash rate acceptably. Upgrading the dome light inside helps a bunch, too (festoon bulb). I get all my bulbs from www.superbrightleds.com
by the way. Great company.
Advice regarding the strength of the KM-145 manual that's behind the stock four cylinder engine is solid. One thing many mechanics and shade tree folks overlook is the absolute importance of keeping GL-5 gear lube OUT of the manual box. It requires GL-4 (Redline MT-90 on Amazon is my go-to) to avoid deterioration of the brass synchros used in the older designs. Pay strict attention to the distinction in the factory service manual about which system uses GL-4 and make no substitutes.
Since you're in mud country, try to keep an eye out for a junkyard first gen with a limited slip rear end, identifiable by stickers in the cab or on the diff advising the use of an additive to use in the pumpkin for the clutches within. Your V-6 model(s) can even use a Gen 2's air locker, although it is a couple of inches wider, but it barely shows. If you do ever upgrade it, get the Gen 2's trailing arms and the coil springs - it'll ride even better since the Gen 2's springs are progressively wound and make it ride like buttah.
Don't settle for just flushing your radiators. As long as they are the original all metal ones, you can and should have them rodded out by a radiator shop. You just can't flush them enough to clean the individual tubes in there. Our local shops do it these days for a touch over $100.
Party on, Garth.