Tyre Pressures

Your handbrake problem is not the calipers. If it was you would have dragging brake pads all the time.

Your problem is most assuredly the two (or just one?) sheathed cables that go to each caliper. Check them for interference or damage to the outer covers that may have allowed water to intrude and rust to form. Removal is a bit of a PITA but once removed you can attempt to free them from forty years of dirt with the penetrating oil or solvent of your choice. If that works, great. Put things back together.

If it doesn't work? Well, you had to remove them to install new ones anyhow.

Larry

I should have mentioned that the cable is free moving and the Calipers have been reconditioned.
the old springs compared to the new ones were a different shape, due to age I suppose, and they are now bringing the actuating arm fully back,
after fitting new return springs.

Still looking for standard tyre pressures.

Peter,

This link has tire pressures.

Pantera Height

Jake

Jake thanks for the link, you would think its an easy thing to get the tyre pressure info, but I struggled, I notice the spring rates are also much higher on the GTS, I wonder why for they were just road cars after all.

good man you.