if the rounded nub clearance is OK what I would do is get (2) brass inverted flare plugs from the Edelman cabinet at your parts house & remove the lines from the MC & cap the ports then idle it & if the booster & check valve is fine and the MC is holding pressure & bled out the pedal will be rock hard with virtually no travel and the prob is downstream (air). if you have a pair of junk fittings/lines you can cut the tubing on em right at the fitting and hammer it shut & screw em into the MC to cap em for the same effect which'd save you a trip to your parts house. & if it ain't high and tight then something is fubared with the booster or MC. EDIT on that prop valve pin iirc you hold it out with a clip when bleeding