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.