Just for clarity, you are talking about the transmitter for your radio trigger (transmitter plus receiver) set, are you not?
For the C33 the PC socket on your lens is where you plug the PC cord that is, at the other end, plugged into your transmitter.
The synch on all Mamiya TLR lenses is entirely mechanical, so you can safely plug even high voltage trigger flashes into it.
That being said, none of the radio triggers I have ever seen have high voltage transmitters.
What you do have to watch for with those triggers is whether or not the receivers can handle the trigger voltage from your flashes.
One further hint - make sure that your Mamiya TLR lenses have the synch set to X - if it slides toward the M setting, your shot won't work.
There is a reason that a lot of wedding photographers used to shoot with Mamiya TLRs where the synch switch had been permanently glued on X.