What model D4?
Still trying to figure that out. Rear serial plate covered by winch, engine plate is missing. I've cleaned the block where the engine plate was, but can only see a couple partial numbers. Going to etch the area to try and raise the rest of them. Even if it works, I'm not sure the engine was never changed.
I ordered an operators manual for the 6U and 7U models, seems accurate for mine, 24v direct electric start, not a conversion.
6U/7U is close enough. Takes #3H2033 glow plugs. Check ebay or Cat for that part number.