Starlight, I've done 'em both ways. It's easy enough to throw some plastic drop cloths over the frame, and mask it tight at the bottom edge of the cab.

Old trucks are always a lot of work. I just helped a friend with all of the body work, primimg, block sanding, then repriming on a 1950 3-window.

The biggest reason they are sooooo rough, is that they are work vehicles, and no one ever takes care of them. They get used and abused until, one day someone wants to make a nice truck out of them again.

If you do it off-frame, you need several strong backs,to move it, or a "body dolly" to set it on so it can be rolled around. I'd loan you a dolly, but you are a little too far from Tucson. :-)

If you decide to paint it apart, you will need to pick a solid color with a simple formula. Keep the paint well mixed before spraying. You may not get the best match this way, but the alternative is to shoot the inside of everything, put it together, mask carefully, and shoot the outside.