The DIN retainer should be easy to remove with a 6mm long reach allen wrench.. You should torque it to 22 ft lbs when you re-install it. Be sure you get the allen wrench full seated as if you only catch about half of the allen portion of the retainer, you will strip it out leaving little chunks of brass in your first stage, which will requrie you to disassemble it, reclean it, change the seat and o-rings and replace the retainer. It is one of those things you will only do once.
The same torque specs apply for a yoke retainer. A large cresent wrench also works, but people using 12" or 15" cresent wrenches are how the yoke retainers on the Mk 20's got over torqued in the first place. Peterbuilt sells yoke nut sockets. They are a little shorter and thinner than a normal 1" socket and for the $20-$25 they cost, they are worth getting.