So out with the angle grinder and cut out the front face of the pedal box as so:
Then prepare a new piece of steel with same hole centres but with a larger hole to accept the Sierra Master Cylinder and weld it on. We had to get the new plate a low as possible to ensure that it cleared the nose panel. After a bit of fiddling about I realised that tilting the top of the new panel back away from the pedal box by about 8mm not only gave more room for the nose panel but also got the reservoir closer to "level"