That looks more like the spot for one of the water temp sensors. I dont know which one, but theres only two.
As for the AC sensor in the water elbow, you need to pull off the sensor from the other elbow and find out what thread it is. Im pretty sure that its a straight thread that seals on a copper washer. So you would need to drill, tap, then get a flat sufrace to seal against. Pipe threads are easy, they just seal themselves.
Dude, for the belts, I would think they are the same as gen2. I used a alt. belt from a non AC 5sfte engine with a modified tensioner. I would bet $20 that the belts that came off your gen2 will fit the gen3.
YES, it does matter which wires go the the THAM etc. Just match the + to+ and the - to -
You will need to swap of the connectors for tham and tha from your st205 harness. You keep the st205 sensors, and splice the connectors into the 185 harness....actually the 185 may fit....try it out.