the kit you listed should do :
2004 Mercedes SL Class
With R-134a Refrigerant
but JIC, here's the low side valve on fleabay :
Mercedes R172 W203 W204 W209 Santech A C Schrader Valve Core Low Side 0008320285 | eBay
and the high side ( same vendor ) :
http://www.ebay.com/itm/Mercedes-W202-W203-W209-W220-W221-W463-S600-A-C-Service-Valve-High-Side-SANTECH-/170808608324?vxp=mtr&hash=item27c4fc8644