I used what I had available in scrap parts at the time I needed it, a little crude but it worked.
A piece of aluminum plate slightly larger than the master cylinder. Tapped a fitting into the center of the aluminum plate for my home built vacuum/pressure bleeder. Two holes at the edge of the aluminum plate outboard of the master cylinder with two bolts through the holes down to a piece of flat bar under the master cylinder. Cut a gasket from some scrap rubber and tightened the bolts. Removed the tubing from the fitting after bleeding and the spillage of fluid when removing the plate was minimal. I did a complete rebuild so I pulled a slight vacuum before adding the fluid and the bleeding required was minimal.