Dave Kimberley and I fitted a concentric clutch slave cylinder from Tony Tewsons Quarter Master company (01926 424609) to our hillclimb Caterham VX. Upon supply of exact dimensions Tony supplied a correct size mounting adaptor. Dave at Demon Tweeks can advise and sells the correct size master cylinder, 5/8 I think. Master cyl has been fitted to into standard pedal box alongside,but slightly higher than the twin brake master cylinders. As Peter Carmichael points out, it is neccessary to fit a positive stop to prevent overthrow- I think I used an 8mm x 130 bolt to do this and just set it by adjusting the stop to when the car could just be pushed when in gear and pedal depressed. The pedal pivot was not altered but a yoke was pivoted on the pedal to line up the operating rod with the master cyl. Works superbly with just the right weight and travel and is giving much more control over starts with very smooth take up compared with the cable.
Incidentally the Quarter Master twin clutch plates in the Sachs 5" clutch have given excellent service and little detectable wear with double drives for a season of hillclimbing. Just a pity the cam belt tensioner was not as reliable - but that is another and rather expensive story !
1.8 SV160 S7OMA