473k, that's got to be one of the highest mileage original motors around. A new one built now and run with modern synth oil probably would last forever but using old style dino oil it seems like they would usually be pretty tired well before that point! The highest I have seen on an original motor was a 244 with 330k -- it finally blew a head gasket. Not bad even so...
Didn't see if you mentioned whether it is a wagon or a sedan? And are you sure it is an '86, or a 760? 1986 was final year for diesels and only was available in a 740 with automatic trans. Previous years you could get a 760 diesel but not '86, if '86 is right then it's probably a 740 even if it somehow ended up with a 760 badge on the back. No great difference either way of course...
However, those final year '86 models are the best of the breed in a number of ways, they had some improvements that the other years didn't get, such as updated front crossmember with better reinforcements in areas that often crack on the earlier cars, composite battery tray that doesn't rust, various electrical updates, etc. As long as you don't view the mandatory automatic transmission as a downside, those final '86 cars are nice to own, with a few less things to worry about if you can find one in good enough shape to be a keeper... Otherwise their parts make nice upgrades for the older ones.