Need help from an OM 617 expert

Last week I went and looked at a NA 617. Owner thought it was a 84 with about 134K miles. Motor #617 912 12 087 454 - can the year be varified with these numbers? Also noticed a few differences:
Head bolts are a star pattern, not allen head
A/C was on drivers bottom, not passenger top.
Alternator bracket, and thermastat housing are slightly different then my 78, 617
Injector pump had this assy, behind ADA. Not sure what it is
Throttle linkages on valve cover are slightly different than the 78
Oil filter housing, and cap had same part # as the 78

Overall did not look like a hard job to get to work in a 78. Is this a Euro motor? Would it be worth $500?? Tranni is shot, from all my research the 78 tranni should work, just have to change kick down.

The motor on my 78 300CD is consuming a lot of oil, when driven hard, not to much when putting around rural roads. Just replaced valve stem guides, did not help. Looking at swapping the 78 OM617, with the 84?? OM617. What problems, if any will I run across??