Agreed, for anyone who has no original AC harness, chasing that RPM feature does not make sense, including PNZWGN. As I had to figure out how to feed W463 300GD tach anyway, I now have the signal, harness and module, and that is why I picked MB compressor and bought that up.
For coolant, aluminium core is definitely better but as I wrote, I am not sure about that integrated oil pipe, and only using that. Maybe summa summarum it also comes out top, but 350GD and G300DT all have extra oil coolers and also all later modules have this extra oil cooling brick on engines. At the moment I have not yet figured out a place where to put extra oil coolant on my build if there is aluminium radiator. I will keep those parts, maybe one day I venture into getting OM606 or if something happens with current engine I do not feel like rebuilding OM617 up makes sense. A thing I understand half way in project, just finding parts for this oldie has become bit hard here