I have found that the Stant Pressure testers help alot in pressure bleeding the air out of the system. Just by pressuring the system, you will hear it belch and fart air out. For me the kit was a great investment and now I pressure test every car that I work on to find hidden issues I never knew were there.
The Pantera is a strange bird for most Americans. So much is different not to mention the heat tubes running under the cabin. The bad early gauges compound the issues, early reports of overheating and general paranoia are all part of it.
Google 50/50 anti-freeze charts that show the boil over points vs. the pressure in the system. That will help you understand more of what the engineering design in the Pantera is doing. It's just a very early version of a high pressure system that is now common in production vehicles.
220 running at idle is ok. You will see the temps drop as you drive it. It's a strange beast and once you learn how it works you will love it. The redesigned radiator on the L cars helps the system quite a bit. It's really going to be the earlier non-updated pre-L cars that may still need some help?
I now pressure test ALL radiator caps. Even new. If they aren't holding the design pressure, then you WILL have boil over issues. On the Pantera you can have a mismatch on the radiator cap and the fill tank. There is a European neck and an US neck. They won't match and as a result you could have zero pressure in the system.
I've seen so many cars with bad caps and they get completely overlooked. I've seen a bunch bad new right out of the box. You need to test the cap and you need the Stant kit to do that.