I'm a glassman and I've done the conversion to the 1 piece door glass on these pickups. It's not overly difficult, I believe you can use the same regulator but with a longer bottom glass mounting channel. The one I did several years ago I put in power windows so I didn't have to fuss with it, but if I remember right, it can be done with the stock hardware.
Once you gut the door of the vent windows and all the channeling and weatherstrips/fuzzies, I think it's the same shell as the earlier ones where they only did have 1 piece of glass in the doors. I can get channeling in 6' sticks and up, and that's what I used for the run channels. Same with the horizontal fuzzy strips, cut and fabricated into the correct length and shape from stock lengths.
Like I said, I put power windows in it so I didn't use the old regulators, I'm kinda speculating that their stock positioning in the door will work. If anything, you may have to move them forward a couple inches.
I would recommend doing the fabricating for the regulators and the channeling, and then build a "window" out of 1/4" masonite or something similar that you can whittle into the correct size and shape of glass that you're gonna need. I have the factory patterns for the stock glass, and could send you a template of that to start with, then you can cut some off the bottom till you have the right height, then send it back to me and I'll cut you some glass for it.....
If you have any specific questions, send me a PM! I'll be glad to help if I can.