I betcha it won't gravity bleed either. If it doesn't, it is getting air from somewhere. Since I moved on from VW bugs, I don't think I've had to R+R a BMC. Anyway, was the BMC taken from an intact system or off the shelf? Tighten the fittings again. Take the MC off the fire wall. The lines should support it Carefully tilt the MC toward the fittings. Fill the reservoir. Leave the top off. Open a bleeder. Eventually it should drip.
Volume 2: I replaced all the lines on the Rat. The whole time, I kept the ABS happy by keeping the reservoir in the MC from running dry. I probably used a qt doing so. I capped the work and filled the system over night. When I replace anything, I hand tighten everything as I make up . It is the way I was taught to do it. Then go back and tighten everything in proper order. In brakes , that is working toward the wheel cylinders. After the final fit, I chased the drips all the way back
Just had a thought, Pump the pedal by hand, feel for how much play there is before you feel pressure. There may be a different push rod length.
Please post the results, TIA