[ETsC10]

I don't know about retro-fitting from another vehicle, but I might shed light on aftermarket.

You may want to start haunting ebay for older add-on units for campers, etc.
I had a neat, self-contained unit (didn't need anything but a supply to and from the radiator),
earlier this summer, that was designed for a camper. Oldie but goodie. I sold it, but there
may be more out there.
I have no idea what brand it was.

Other than that, I had a Mohave heater & plenum that I also sold. I would think they probably
run under $300 and will give you everything you need, other than controls, and still fit under the dash.

Good luck on your quest...subscribed.