Tempur,
For the 230SL, the fuel pump exchange is pretty much a direct exchange. The top portion of the original pump bracket is still used and an interface bracket is used to attach the newer style pump to the bracket. I've seen some where they attach the new interface bracket directly to the car frame as well. In either case, the protective cover for the older pump will not fit due to the arrangement of the hoses. In order to be used, it would have to be cut to allow the hoses to pass through, or you would have to find a cover designed for the newer pump. When using the newer pump to replace an older pump on a 250 or 280, there is an additional hose that must be fitted with a tee fitting to the small bleed fitting on the pump--the one closed off with a small screw. Not sure exactly when the pumps changed over, but unless there is a stash of these older pump somewhere in the "National Re-doubt", new, old style pumps are NLA. Hope this helps
George Des