the last time i bled the clutch on my 75, no matter what i tried, i could NOT get it to bleed by conventional methods.
eventually i back bled it. get a pressure bleeder & take off the cap which goes onto the master cylinder, attach the end of the hose to the bleed nipple & apply the air pressure and slacken the nipple.
take care tho, firstly, unless the hose is a tight fit, be prepared to hold it tight onto the nipple, there will likely be fluid spill around that area. if i'm backbleeding, i normally use a tyre with 10-15psi, much over that is too high.
also, it is pretty certain that fluid will come out of the reservoir, it's best not to remove the lid, but place rags/ newspaper around it to protect the engine bay.
it's best not to keep the nipple open too long, but on stubborn airlocks sometimes you have no choice.
if this doesn't work, and you can't get a clutch, then i'm afraid it seems something has gone amiss during rebuild, or simply the cylinder has chosen that particular moment to fail, it wouldn't be the first time i've had a hydraulic cylinder "run home to momma" when it's been disturbed !
the first clutch i ever did was a capri. i took the box out, replaced & aligned the clutch, then put everything back together. the whole thing took around an afternoon.
i stood back to admire my handiwork, chuffed at my first major job completed in a reasonably short time. back in those days, i used to smoke. i put my hand in my pocket to get my cigs.
AND PULLED OUT THE RELEASE BEARING !!!!!!!
it didn't take quite so long to re-strip it.