Look on a custom wheel website or perhaps www.tirerack.com. Tire rack have a lot of great information. Perhaps contact a specialty Mercedes wrecking yard and ask them what wheels will fit from one Mercedes to another. Wheel offset is important so as to clear the brake calipers.
Your S420 stock rim is 71/2 wide with an offset number 51 and it's a 16 inch rim. The lug size is also larger than most of the older or smaller MBZ vehicles. Be sure you verify these things before you install tires on the rims just to find they hit the tie rod ends, calipers and/or control arms.