Ok, this is an early 70's small block 318 intake and the red lines show the possible locations for a temp sender.
Senders can vary in size also, so first you want to locate a threaded opening that fits your sender unit and is as close to the thermostat as possible.
Basically any one of the ports in this picture with the red lines could be used.
Remember, the closer to the thermostat the better and you don't want adapters if there is any possible way to avoid it.
On most manifolds, anything forward of the first high spot on the intake (runners) is going to be coolant and any holes on the back are going to be vacuum ports.
Some intakes, like the one on the Wife's car I had no choice but to drill it and tap to a bigger size because there was only the one small port available.
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