I was told it could be the inhibitor switch or NSS, is there a way to bypass it or adjust it?------------this is completely wrong. the nss in a benz acts just like any other. allows the starter to engage when the shifter is in p or n---nothing else.

only place for a rev limiter is here-

https://www.ebay.com/p/MERCEDES-BENZ-300-SL-MAS-Control-Unit-Module-0125454832/1022976863

it controls spark and fuel with the ecm. not saying it's the problem, just needs more diagnosis. check engine light on? it's tough to tell, we can't see under your hood, the light here sucks. good luck, chuck.