There is a little tool they package with the valve bodies that I got when I ordered replacements that can pop the core out. I have since replaced the entire manablock with a hot and cold copper manifold I got online.
https://www.supplyhouse.com/Bluefin-...ree-10-Outlets and the right side...
https://www.supplyhouse.com/Bluefin-...ree-10-Outlets
My block cracked at the #5 valve where the valve core fits into the housing and would not stop even when I moved the line to the empty #6 port. At about the 9:00 position in the closeup pic. The blue cylinder is a replacement valve body I had ordered for another port.
I removed the panel that covered all of it. Added the pressure gauge and a line to a 2 gallon pressure tank between my frame rails near the fresh tank. Added the bar light and there is a remote controlled water valve(above the gauge) in there to supply a misting system for the radiator that I put in before I knew why I was over heating on hills.