[Mart]

On the subject of adaptor caps for oddball cylinders.. You don't actually need a screw fitting cap. I have used a flat piece of plate with a npt hole drilled and tapped in it. I positioned the plate over the hole using a piece of rubber cut from an inner tube and clamped the plate to the top of the master cylinder.
Once fitted, just proceed as normal with the pressure bleed operation. As they say: "It worked for me".
Mart.