You can't put anything bigger than 4x6s in the dash without a chainsaw. By 6-1/2s in front I mean in the doors if you use the door panel frames from an 88-up W126. Just find a junker that has the same color interior. It's your call whether to use the entire replacement door panel with pleated leather or put the frame over your door panel with perforated leather.

The dash has 4x6 openings but there are defroster ducts in the way so you can't fit speakers with large diameter magnets. I got some Polks hoping they'd improve the sound. They probably would have but I'd have had to hack the ducts. Rainbow brand 4x6s that are highly recommended for W124s might fit. I don't think 4x6s come deep enough to use the vertical space in an SDL dash.

Sixto