mag thermostat housing?

Very true
Manifold only has a (qty 2) 1/8 NPT spot for an electric gauges.
The guy that designed these manifold must not have been a car guy to include an extra 3/8 npt hole.
The factory gauge does still work, I just like the accuracy of aftermarket analog mechanical gauges, this engine is going to be used for towing, so redundancy is nice, like in aircraft's.

I'm still unfamiliar with gauge connections...would this gauge work? I've got the same manifold going in mine.

http://newvintageusallc.mybigcommerce.com/2-1-16-water-temp-250fw-sender/