The 126 is longer than the 108, but both fit in the garage (and I can close the door too!!!).
You don't say which engine you'd be getting if you made the jump to a 108, but with the 4.5 you don't have mechanical injection you have early EFI. The 2.8's had mechanical injection.
The 4.5 last year averaged 12.81 MPG - mostly city. Had a high of 15.9 MPG on the trip to Lost Wages. Not a gas saver by any means and you don't want to be caught too far from a filling station when the idiot light comes on.
With an older daily driver, be prepared to spend some bucks in in upkeep and repairs. If not a DIYer, I wouldn't suggest a 30 year old car for daily use. Last year I logged 9K miles, spent $1100 on fuel and $1500 on parts, and did all my own work. Throw in insurance and I spent $.30/mile to enjoy the old gal, or $225.00 per month.
I have been driving the 560 for the past month. Today I took the 4.5 to work. I had forgotten how fun it is to drive that car. It starts in 1st gear and launches off the line in comparisson to the 560. This afternoon I took the 560 out and played with manual shifting, found I could launch about as quick as the 4.5. But, lauches like that make you stop at the filling station more often.
There are still a number of 108's running around town, one local shop still works on them too. They will run and run with the proper upkeep. Yes, there are fewer electrical gizmos, which makes things easier. Most of the mechanicals are still available, but body parts and trim pieces are getting harder to find.
I guess it all boils down to - what are you comfortable doing Paul?
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.