I just used the front of the Master cylinder to do the front brakes, with a t-piece. Then the rear of the cylidner to do the rear brakes. Bias valve inline, job done.

My bias valve is mounted similarly to Jambo's, but more tucked under the seat. It's actually bracketed off the same chassis rail that the seat bolts to.

Incidentally (blatant plug), I'll probably be selling my entire Servo/Master Cylinder assembly soon. It has a 25mm recently rebuilt Master Cylinder (the 25mm cylinders are like rocking horse shit and I got one of the last rebuild kits before they were made obsolete). It also has the correct reservoir fitted without the additional ports on it.