When I did my Sumo I used a Cortina master cylinder. It was the other way round to yours though with the two outlets at the front and the single one at the rear.
The twin outlets fed the front brakes, one for each side. The single outlet for the back brakes. The pipe for this one goes to one of the rear cylinders and then back out again to the other rear cylinder over the live rear axle, hence why only needing one outlet.
Hope this makes sense.
John
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