From forum posts, I understand that MB improved the quality of valve stem seals on the M103 and timing chain guides on the M117. If my 91 M103 is any indication, the new valve stem seals aren't good enough
Also, MB went from KE3 to KE5 Jetronic. I don't know if the engine designation changed.
BTW, I didn't mean to trample on your right to do whatever you like. I could have worded better what were considerations, not attempts to discourage you.
And I've done my share of buying a $500 project car, spending $2000 to get it running and selling it for $500.