Ok, so I had another look at the handbrake issue today and I'm pretty sure I know why its not working.
The replacement callipers are not the same as the old ones.
They look almost identical on the outside, same part numbers, patent numbers, size shape etc etc, however on the inside there is a difference, I pulled the pistons out of the old and new callipers and they are identical however the shape of the cavity inside is different, with the new calliper having a deeper 1st section on the inside that the old one.
This results in the different behaviour when the handbrake is applied, in the video below you can see the piston on the old calliper (tested 1st) does not go as far back into the body as on the new one. You'll also notice that on the old calliper the Piston 'rachets' out with every application of the lever and I have to push it back in, on the new calliper it actually does sweet F.A.
http://vidmg.photobucket.com/albums/v223/ryanbudd/89%20IROC/Handbrake%20Diagnosis_zps9ium9jp8.mp4I have checked and there are not any bits missing, the piston bore is machined differently from the casting.
These replacement callipers were bought from Rockauto and are the A1-Cardone remanufactured callipers specific for my car. Why would they be fundamentally different? I don't understand.
Now I have a decision here, Rockauto sell the "same" callipers branded as ACDELCO and Raybestos etc, so do I risk buying more Remanufactured stock callipers in the hope that I get ones that are actually correct, which will cost me probably about £400, but might not work and I'm still left with a Carp handbrake. Or do I pull about £2500 out of savings and go for a full 4-corner Baer setup which is a MUCH bigger job, but would give me a handbrake that works properly and better brakes all round?