Thanks, ya'll. I'll answer some specifics, and pardon me but I don't know how to work a multiple-quote thingy (yeah, I'm a computer dumb-ass).
MountainMike- I used a siphon-cup spray gun (I believe that's what it's called); you know, the sprayer with a 1 quart cup on the bottom. It's a Matco brand I bought in the 80's. I painted one car with it, and it had just sat in my tool box since. I can't believe it actually still worked.
CopyCat-
Yes, I reduced the paint. Carefully follow the recommendations on the can. Per each quart from the can, add 2 oz. of hardener, and 2 oz. of Nathpa (for spraying; mineral spirits for brushing). Use a measuring cup and be precise (I "borrowed" one from the kitchen; if my wife reads this I'm dead meat).
Yes, it is the Valspar Tractor & Implement high gloss enamel paint sold at Tractor Supply. It's the regular stuff, at $29.99 a gallon. I was going to buy the $45/gal Premium paint, but my local TSC didn't stock the high-dollar stuff. So I got the regular tractor paint. Hardener does improve the gloss, from what I was told.
Your understanding of painting is really the same as mine. I put it on as thick as I dared, and went back over it a few times, in two separate spraying sessions per color. I paid special attention to high spots and panel edges, to make the paint thicker in these places. I totally stripped the body for this one; the next time I can get away with tape-masking a lot of things and not having to disassemble as much stuff.
kkjb4x4.0-
I'm not an expert body man by any means, but I fixed several dents for this paint job, including a little panel rot behind the rear wheels. You just have jump into it to learn it, and rocker panels are a real good place to start learning bodywork. Just remember, you've got to get ALL of the rust out, or it'll come back.
I'm floored by all of the positive, and kind, responses. I mainly wanted to encourage you guys, with a similar old truck, to just go for it. All it really takes is some time, patience, and care, to turn a sow's ear into a silk purse. Believe me, if I can do it, then anybody can paint their own truck. Good luck, and keep on truckin!