I agree with swapping all the Rubber parts. I would have done ALL the rubber hoses when I did the calipers. Can't trust 30-40+ year old rubber. And this may be silly but- check to make sure your bleeder valves on the calipers are pointing UP when the caliper is installed. If they are pointing down you will be bleeding them until the end of time and never get all the air out of the system.
It is possible to swap left-to-right and end up with them pointing down. Got this from the gurus of the brake swap..thanks E-boog!

Other than that- I'd replace the master cylinder, and check the proportioning valve. If it is corroded and leaking you will never get all the air out either....

Good Luck with it!
CC.