I think you would be money and definatly time ahead to find a shop. I would not recc. adjusting the 3mm mixture screw if you are not going to do it right. Running the engine too lean or too rich will destroy the Cats. Thats some good money right there. If the funds are tight, try looking for a mom and pop's that will work with you. Or, you could call the local MBZ dealer and see if you can talk to a tech, or maybe even service can help you out. Ask if anyone was ever a tech befor they were in service. Hope the advise helps, I would explain it, but I think it would end up costing you a lot of money.
GVB