Sorry Jim, I've only just noticed your post. Not sure if you're referring to the thermostat housing or the heater hose fitting, so I'll give both.

Thermostat housing: Aeroflow - not sure if there available in the US? https://www.aeroflowperformance.com/...mostat-housing
Heater hose fittings: Speedflow - again, an Aussie company. Sorry, I didn't note the part numbers.
I made a puller to remove the pressed in fittings:
20191219_1.jpg 20191219_2.jpg

Then threaded the holes to 1/2" & 3/8" NPT. Neither needed drilling but i do recall one of them was fairly tight and needed a lot of fwd/rev with the tap to get through it.

Front fitting is 1/2" NPT x 5/8" hose tail, 90 deg.
Rear fitting is 3/8" NPT x 5/8" hose tail, 45 deg.