I don't have an original mic, but the pinout on the stock mic and 1/4" stereo type phone plug should be the tip is the audio and probably white. First ring is PTT and probably red. Shank ring should be ground and most likely black. If there is a shield, it's connected to this too. The centurion is 3 wire relay switched, so their should be no need for audio switching or a spdt pair on the ptt/audio contacts.
The mic according to the schematic is not switched from open to closed during transmit although it shows a switch contact on the stock mic, the pins are jumped, therefore direct. This is for the PLL40, but should be exactly the same as the 23 channel centurions and the 40D since they all used the same mic wiring.
I have no schematic for their power mic, but it would be exactly the same.