Rover V8 (14CUX injection) brake servo fittingto plenum, anybody have a part number?

[GDCobra]

A while back I rigged up a brake servo to my car and simply added a fitting to one of the bungs of the plenum base which should be OK however I'd like to use the correct fitting for this and just wondered:

1) If anybody has a part number for this, and

2) If this fitting is simply straight through or contains a one way valve (to maintain vacuum in the servo as the throttle is opened)?