You can mount the gauge sender in either head and the reading will be about the same. In my experience, it's been about 10 degrees F higher than the temp measured near the water neck.
I've found both locations to be accurate for what they're measuring. If you mount the sender in the head, you'll get the temperature of the water in the head. If you mount it in or near the neck, you'll get the temperature there.
I've gotten used to readings in the head, so I mount my gauge senders there on V8 motors. It all depends on what you want to measure...but for me, knowing what temp a motor usually runs at and then checking for deviation from that is what seems important to me.
I have the stock gauge in my 64 C10 (292 I6) and it doesn't even have values on it...just C and H. (I think.) But I know that when the motor is warmed up, it reads about 1/3 of the gauge. It never goes over that. But if it did, I'd start to get concerned.
Again, this is just my opinion. Your mileage may vary.
