I've never had one, but I think an M103-based W126 would be killer. Good performance, decent fuel economy, and best of all the M103 is very easy to work on and would have plenty of clearance in the larger W126 chassis. The W126 has timeless lines and, since a large number of them were in use not only here but around the world, parts are very inexpensive.

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280