copper wont be just fine. It will fatigue and just crack when you least expect it , it cant handle the vibration and movement of the driveline
if you want to bend your own use steel or stainless , local parts stores should have 5/16 tubing with correct ends but they normally dont carry lenghts long enough to do tranny lines in one peice
inlinetube.com or classictube.com can supply the raw tubing or ready to use prebent lines specifically for the turbo regal
With the motor in the car it might be almost impossible to put a one piece bent tranny line in place. I had to replace one of mine d/t it tapping/resting on the frame for 18 years. I just used two steel tubes and a brass coupler to join them.