We are here doing a complete rebuild of a 1981 corvette (in Australia), so usual problem of thousands of parts and not enough photos of how things were put together :-0
So I'm stuck on the power locks, I've got it physically working, I'm just stumped as to what this third rod is used for and what it connects to?

 

Since my 73 does not have power locks, I'm afraid that I cannot help you. I would recommend getting a copy of the factory service manual to see if the illustrations there could prove beneficial. Those are available from Helm or some of the Corvette aftermarket suppliers.

 

That is the manual door lock rode that the chrome-plastic door lock cap screws to. it goes through the door panel via the hole at 12:00 of the arm rest on both doors. It allows the driver/passenger to manually engage or disengage the door locks, say, in case the battery was dead.