I've got the stamped metal / tube T-stat housing, so not near enuf thickness
to drill and tap.
I know they make them with a threaded bung, but they're something like $30 or so,
plus all the work with the fan etc.
Was hoping there was another port on the block or head someplace.
I've got a "water sender attachment" on another engine and it works fine, and is easy to install. It's an aluminum tube that you put in your upper radiator hose, with a threaded port for the sender. About $20 on ebay.
Just do a search on ebay for "water sender attachment"
It doesn't register much of anything until the T-stat opens, but I guess that's when it's most important to know the coolant tempanyway. If you put it in the upper radiator hose close to the T-stat, it'll show you the temp of the coolant just after it comes out of the engine.