Well you have the early tranny and the B2 piston I carry will NOT work in it. Mercedes has redesigned the piston and made it shorter, requiring you to have a longer push rod and new cover. You will have to get a tranny shop to do the job, because it must be measured and fitted to work. Sorry about this news.
Hey, if you want straight, good answers talk to Henry Schuman of Schuman Automotive. www.schumanautomotive.com. They guy has YEARS of experience working on Vintage Benz cars. He can usually get you parts at a good discount. There is a forum over there too.