Any chance of getting pics of the calipers mounted on the car front and rear.
I don't think that you have a master cylinder seal issue.
I can think of three easily possible issues.
Master cylinder pushrod length. Make sure it has some play in it as Mike mentioned. Generally, adjust as long as you can freely install and remove the pedal attachment pin.
Rear caliper bleeder orientation. Could you unbolt the caliper and use the gravity method for bleeding and just tip the caliper around a little pointing the bleeder more towards up? I have had to do this before on a conversion that changed the bleeder position from the stock(280zx) position.
Rear caliper parking brake adjustment. This depends on what year/style calipers you are using. This comment will not apply to early 280zx calipers, but the late calipers will be affected by this. The rear caliper pistons will retract far enough to give you a pedal that needs pumped up each time if the parking brake arm is not actuated repeatedly also. I have no idea really how to explain it though.
Take a look at how much clearance you have between the pads and the rotor on all pads, inner and outer, top and bottom. They should all appear to be touching the rotor with basically only enough clearance for the rotor to turn.