How long can 616 or 617 go without rebuild?

[shertex]

As a "fun car" (not that all of my cars aren't fun), I'm looking at a 1983 manual 240D. The odo is broken at 205K, but Autocheck shows a mileage of 217K back in 1999 (definitely a rollback in its history). So, realistically, this car probably has 350K on it, give or take. But it drives fine....and it's fun to drive a manual.

So how far have 616 engines (and 617 for that matter) been known to go without a rebuild? I wouldn't want a fun car suddenly to become un-fun.