Due to the alignment of the servo with the brake pedal, which seems to vary from car to car, and has caused some owners a problem with using a clevis, it is a good idea to use a rose joint instead to connect the pedal to the new servo.
The correct rose joint is a 3/8" x 3/8" female right hand thread rose joint. Patrick sourced his from:
http://www.ebay.co.uk/itm/180425540596
They sound good quality, and are remarkably good value at only £9.50 including postage.