I have done the b2 piston with the trans in the car on a 83 300d.

drop crossmember lower trans and push to one side.

remove cover, piston should easily pull out by hand or with pliers.

not much room

mine fell out in pieces.

be sure to replace the cover seal ( don't ask how i know)

i did not remove the pan

be carefull not to drop the pin behind the piston or you will have to remove the pan to get it.

cleanliness is very important!!

have fun enjoying your properly working tranny!

Steve