This one will require you going out and opening the hood of your MGB in this cool fall weather!
I need to know what size brake line fitting, nut, you have on both outlets of your dual master cylinder, and where those lines go into the 4 way fitting. These are the two lines out of the M/C that go to to the 4-way union. I took a quick look at my 72 MGB/GT, it appears to have two 7/16" brake line fittings on the outbound lines.
One of our UK suppliers says one of the lines has a 1/2" brake line nut on one end, (with a larger fitting) going into the M/C. There is an adapter on the rear fitting, but it adapts to a 7/16" fitting.
I need a consensus on this, your assistance is much appreciated. Thanks