Regarding the thermocouple position. A pretty accurate reading will be obtained if you move the thermocouple to the back of the cylinder, second fin down from the top. You can use the cylinder screw access holes to clamp the wire in place by running a short hex head screw and bolt into the hole, and using a couple of flat washers as clamps on both side of a fin. This has been done on about a thousand engines that I'm aware of and it works just great.

If you have the ability, attaching at the base of the spark plug is the best, but as noted before, not always possible.