I don't mean to sound harsh but you are really flying blind without the correct factory service manuals.

They are dealer only items but there are quite a few available on e-bay these days, all the information is also in the W124 CD but I find the CD versions of the manuals a royal PITA.

There is currently a 602/603 engine book on ebay. It does not look like there are any serious bidders at the moment.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2471118981&category=34227