I had this exact same problem with my 69 corvette. There are two bleading methods you can try.
1. Gravity blead method. Open one bleader valve at a time keep the master cylinder full, watch the bleader hose in the recovery bottle on the floor, when the bubbles stop, the caliper is free of air. Use a clear container so you can see if fluid is flowing out of the bleader hose.
2. Sometimes this does not work. If you have debree in the line or old flex hoses that have swollen up, gravity bleading doesn't work very well. Buy a $6.95 one man brake blead kit. This is a hose and recovery bottle that is designed to work without closing the bleader valve every time you let the pedal up. The trick to this is to have your recovery bottle HIGHER than your caliper. Pump the brake pedal 10 to 15 times for each caliper. Start with the longest brake line and work to the smallest. If you have a caliper with two blead valves, blead the inside one first then the outside.
3. If you still get bubbles after this, you are pulling air in somewhere in the system. Fill the master cylinder, pump the brake pedal up several times to get as much pressure as you can and have someone hold there foot down on the pedal, or if by yourself wedge a 2 x 4 between the brake pedal and the seat to maintain pressure on the brake system. Get a mirror and your best light and check every inch of the brake line for any fluid leaks. If you discover a leak, this area will also pull air in when you let off on the brake pedal. Hope this solves your problem, let me know what happens.