Autozone may also have the pressure test/bleed tools for loan. I ended up getting a kit from Amazon as my kid has a 2003 Land Rover discovery with the always blown head gaskets. It can pressure test, but it can also to a bleed the air out of the system. If you are in the Los Angeles area you are welcome to use the test kit I have, I think it has adapters for all types of Radiator caps.
I had an old stock 65 mustang with a 289 that had the same issues, changed pretty much everything in the cooling system at one point but in the summer could never get it to not boil over when stopped. Chalked it up to engine issue, timing, head gaskets, never could nail it down but was not the cooling system parts. Motor had been rebuilt at least once.
Last comment is the Griffin radiator is likely the least effective radiator for the Tiger IMO, I had one and it worked in my stock 260 but only got it because my original was in really bad shape and didn't know better to fix that at the time, it was the new aluminum radiator syndrome

The Fluidyne is a different story, I'll find out soon enough I guess.
Also water wetter in Antifreeze doesn't do much, not sure if it actually drops the boiling point, but with antifreeze I never noticed a difference adding WW until I just used it alone, and was not much going that way either. And if you did run WW alone need to make sure it's one that has a rust preventative.
QUESTION FOR OTHERS : I thought the purpose of the tank was to collect the air (Like my diesel has an outgas tank) to ensure things are full. The way the Dale/Fluidyne radiator are plumbed I think that is how it works, but can't remember how the Griffin or Stock one does it. Pic attached of the Fluidyne with the bleed at the top left back to my tank.
Good luck with this, it's a never ending chase!
Sandy
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