123 and 126
123 wheels fit 126 cars. The main difference is the wheel width is narrower on most 123's, and they are all pretty much 14". 126s were 195 70 14 early on then 205 65 15 later.

124
Stock wheel size on a non-sportline, non-500E W124 is 6.5x15, ET49 offset, 5 lug 112mm. Sportline wheels were 7x15, ET44 and only came in the 8-hole (newer) style. These are the only MB OE wheel sizes for the non-mega-car (500E) W124s. - Mike Nowak