See if anyone can make heads or tales of this?

I to have a new motor like a few others on the board that likes to run around 230. it has never boiled over with just a 13lbs cap? However on the highway it hits 230 and creeps a little. As soon as I come to a stop hit the breaks the temp needle will drop to 190 maybe 200. I know this is not possible to just drop in temps like this so I am pretty sure gauge is the fault here. However the electric spal fan has a 180 thermo and it kicks in when the temp gauge reaches 190.

It's just a little un-nerving driving the car and seeing the gauge at 230 not sure why

Anyway could the placement of the electric probe be the issue on the gauge? It is at the back of the Wieand stealth on the driver side.

Not 100% on the timing my friend that has his own shop set it at 10% if I remember correctly the carb is a holley 600 4160 vacum sec. I do have a pro billet mechanical advance msd dist. The car seems to run really good. I do have a frame canister fuel filter and a stone inline??? not sure this is not overkill?? This is not a real hot build though the heads are ported rather well and are stock 65 iron heads. the cam is like 512 and 245 or something close lunati. I do have underdrive crank pulley ( because thats what summit sent I ordered the stock but figured what the hey) but the kit is suppose to have the oversized water pump pulley. with a milidon waterpump. My biggest problem may be the rad. I have a 65/66 northern with a Spal electric fan. I script here and made bracket for this to fit the 67 but my thinking was it's a mild small block 302 and lots of guys run them in the 66 and 65 cars so it should work. Plus it was cheap from a friend. Got the Electric fan from Mustang Plus Both are brand new.