Thanks for the information about the removal tool! I will try 1-st Line as a first step.

Here's a tip for the tool, should anyone rent or buy or make one.
Be sure to place a buffer scrap piece of plastic between the tool's tip that is doing the pushing upwards, to the face of the piston, which is easily scratched from the spinning metal bolt. A poker chip would do, something softer would be even better, polyethylene (milk gallon) offers the right about of slickness to act as a bumper between the two hard parts.

On my DIY tool, I use a socket wrench on a large hex head bolt. I watch for the piston rod at the top of the group to rise, and then work off the c-clips and pins. Reversing the action on the wrench, I can slowly lower the piston to where the pressure is relieved, and then unhook the PF tool without drama.
Just judging from the amount of force applied to the socket, and I'm now looking at the faucet handle of the rental tool, it seems to me that it might be harder than it appears, but, I have no experience using it. The space under the group is tight to the rear, (knuckle warning).