Velcome back, herr Dave,
Is your car the vehicle that Car & Driver reviewed in the early 90s? I bet you fixed that idle problem long ago.
I see that you have an HDJ80 in the stable too. It's on my list of 4x4s to buy when I fine a clean rust-free example. There are
very few in France.
I don't see what could be so hard about sourcing a 560 engine/trans, dropping it in a nice used W124 wagon, and grafting in stronger front springs and brakes. A bigger radiator would complete the package. Here in Yurrup, the stock 560 makes about 300hp. A better exhaust, ignition, and air filter should give about 320. :p
Speaking of which, I recently located a 928S (2v) engine complete with the necessary adaptors to mount it in my Range Rover. But the finance minister (wife) is already a bit peevish about my expensive manual->auto conversion. I slipped in a winch, new radiator, etc under the same budget line item.