The squatness of the master cylinder definitely looks a useful feature, even if the diameter of the servo turns out to make it less space friendly in a kit car.
Peter, have you actually already purchased one of those fancy servos designed to be remoted? With something like this you may be able to just use a slave cylinder pushing the input of the servo to get the same effect but at significantly lower cost. I can see this arrangement fitting sideways in the battery box area of the sportster quite nicely making room for the wide heads of an M60/62 engine