Hello, Did a 70 Challenger last year, and just today, finished a 71 Cuda...exact issue you are having!! 1st the Challenger. If you are using the valves from a 70 (two separate valves) make darn sure the lines are hooked correctly. Believe me, you can hook them up wrong! That was my problem. Could not get the car to bleed. Had a hard pedal tho. Switched the lines to the correct positions, problem solved. Now, the 71 Cuda from today. Kit came from Inline. It is to use the 70 valves. Shouldn't make a difference tho. Anyway, couldn't for the life of me get fluid to the rear. Bled, and bled..no luck. Ended up being a collapsed rear hose. Why it worked with the drum...I don't know. Replaced hose, all's good.
When you are bleeding, crack open fitting closest to master and work your way back. I bet you'll find the problem. Take care, Jeff