To my knowledge, no one is making either heater nowadays. Not the "tombstone" style for the early jeeps nor the fresh air type for the later 3B. The Parts Manual I have has group section:
GROUP 35-21 -- HEATER AND DEFROSTER
but I'm not sure which heater this refers to, but the heater assembly is 669313.
The other post you checked in on may be one of the best as ChuckW did a detailed restoration of a fresh air heater
https://cj3apage.com/Forum/index.php?topic=5234.0Grover's website had a list of salvage yards that was becoming dated back when I used it (late '90s) so more dated now. Living in KS at the time, I travelled down to one of the listed yards in OK and scored all the clips I needed for wiring and brake lines plus some more parts. We talked for quite a while and then I left. I haven't published my story on the heater I got yet but he called me out of the blue telling me he had just pulled one out of a '55 CJ5. My point is you never know where your next needed part may come from. Also get in touch with Harry Sheets.
I haven't seen anyone take detailed measurements of a complete unit. I suspect one day that will be the only way to reconstruct one.
On your donor heater, If 6V, it should run - really fast - on 12V (my square donor heater did). More likely there could be some wear internally. I've looked up replacement motors using NAPA to swap out my heater motor.
Everything should use the body/frame as a common ground - hence the one wire going to everything.