Somewhere around 80, MB started to harden their cam lobes a different way, due to unacceptable wear. A better glow plug system was also introduced. I think a used engine from a slightly newer donor would be your best bet. Paying someone to rebuild that engine properly will almost certainly cost more than it's worth. I rebuilt mine a couple years back, cost me 2K, did over 95% of the work myself. Oh, and I'm nuts.
