Yes, each cable should have one tune. You can see where the cables exit in this picture:
On the right of the picture (left side of the car) you can see a cable exiting near the rear frame horn and going to the backing plate. That is where they should exit. Do you have both exit points on your chassis?
If you have only one tune (be very sure first), then you MAY be able to get away with just one e-brake caliper. My thought is that they usually test the ebrake and one may be enough to hold the vehicle for the test.
of course I am open to alternative opinions.