The most direct route would be a manual trans from an early SLK as these had the 4 cylinder version of a M104 / 6. Given the SLK is based on the W202, the pedal is likely the same. The 90 300SL is an uncommon car, it used the same manual trans as a W201 inline 2.6 6. From other postings I've read, these trans were on the weak side for these motors.

Dig around car-part.com