Might have to do this----I have to do it on my 59 Elky with caddy calipers in the back.Remove the calipers, insert a block, and bleed them at various angles if necessary.
When mounted the bleeder cavity is not at the top so the calipers need to removed and rotated back before they will bleed.
(I hate Caddy calipers---have to adjust the parking brake before they can be properly bled)
Sometimes getting the air out of the lines can be an issue as well.
I generally have issues with the master cylinders. Has you master been properly bench bled??? If not it may never work right.