I would say, as a whole, largely original. As I'm yet to be an owner (only a few more months in this damn country), I can only dream, but I'd probably consider a few options.
- Exhaust. Nothing loud, but surely, as with most V8s, there's something to be had there that can maybe get a bit loud when it's on full song, but stays quiet when driving sedately.
- Suspension - put new springs and shocks (Koni or similar), to drop it just a little bit (not lowrider style or anything, just half or an inch to sit it a bit lower, put it in better contact with the road, and increase the feedback a little bit).
- Steering wheel. Something like the ones in the images below. For me, the wheel is a huge part of how a car feels to drive, and the wheel in the W116 isn't all that special.


Hard to find a good one, but I think the first one would look good.
Other than that, I think Bundts probably look the best, would be nice in a 16" perhaps, instead of 14"
This is one modified W116 I really like the look of. Looks purposeful.