The Range Rover body either on Unimog chassis or at least with Unimog axles has been done. In Finland, of course. I think it had a Chrysler V8, was bobtailed, and shortened. I just looked at two videos of Mog-axled RRCs on U-Tube and neither was the one I'd seen in the past.
I wouldn't mind a diesel so much in my Classic, provided it had prodigious power and torque. I'd be thinking along the lines of the V10 used in the VW Touareg, with its 6-speed tiptronic gearbox, as well. Needless to say, the entire driveline would require major upgrades!