It appears you are swapping out the U.S. bumpers for the Gen 2 Euro ones so the front and rear lips will fit. Locating a decent set of those Gen 2 bumpers is challenging. Please PM me if you know of a reliable source.
I believe the PR Tuning kit is listed on eBay by one or more vendors. Here's one being listed for $2,300:
C126 sec 1983+1991 AM STYLE 6.0 WIDE BODY KIT. FITS ALL C126 SEC MODELS. 20 years experience on developing After market German auto parts. Note: Require professional installation.
Here's another standard or widebody kit from DMC that's made of much stronger carbon fiber material (TUV approved) for those who are not turned off by its cost. This kit comes with the front and rear AMG Euro bumpers with the lip spoilers molded into one piece. You can also mount the side skirts with or without the widebody panels for those who are not too keen on cutting up the rear fenders.