QUOTE
or if I need it all
You don't.
The idea was to get a handbrake on the arms you have now and then put together a set of proper vintage arms (with the proper tabs and cable mounts) for your GT calipers. That way, when you decide to make the switch, you put the original cables in and bolt on the original arms.
Early 911 brakes would be a step backward from what you have now and, your bias should be matched "OK" given what your fronts are [edit: however you may be talking about early 911 handbrakes, not sure. If that's the case; what you have is what you need]. If you were to do something like that, simply get the proper arms now and use the 914-6/GT calipers you have. They have the same pads and 38mm pistons the early 911 calipers would have.
Karl, you're 99% there. You have all the parts you need to make it happen utilizing your existing calipers and control arms as the basis.
You should be able to drop them off with Matthias and have him put it together. Have him call me if he has any questions.