QUOTE(ClayPerrine @ Mar 29 2022, 11:44 AM)
The temp sender needs to be on the right rear cylinder (#3). That cylinder is the farthest from the fan, and runs hottest. Don't try to run the temp sender from the left head. It will make the engine run rich.
You either have to switch the heads, or drill and tap (8x1.0 threads). The boss is there, it has not been drilled and tapped in the left cylinder head.
Clay
If he's only got 1 head on thus far it seems a lot easier to remove it and reinstall on the correct side than to drill and tap. Just be careful with the pushrod tube seals, or if unsure just replace the outer ones. Reinz are only about a buck apiece. First check and make sure you don't have two heads that are both threaded. After 50+ years who knows what might be there?