heat problem

i have a 327 small block. i have 3 options to check the temperature, first there is a position next to cylinder no 8.. then on the intake manifold next to the water pipe feeding to the radiator... then on the radiator itself i had s fitting mounted on the to reservoir.... each of these positions give me a different reading so which is the correct place..... next what is the ideal temp for a normally aspirated motor to run ....motor #V0810CKM

use the 1/2 NPT hole in the cylinder head

The one in the head is best, the manifold one a close second. The rad one is all but useless.

ideal temp is a subject of protracted debate.

Personally, I like 170, just because it gives a bigger window for trouble if things overheat.