Hi, at risk of being accused of K abuse my car has a hydraulic clutch setup at the moment until I can obtain the correct spec C4 trans. It has a later V8 Falcon bell housing to suit hydraulic clutch. The pedal support and firewall has been drilled to suit the master cylinder. This was already done to my car when I got it many years ago but I have done this conversion on a 64 and 65 Futura coupes.
This is easier to do with the pedal support out of the car. You have to drill mounting holes for the cylinder and put a hole for the master cylinder to go through. Weld two nuts on the pedal support for the m/c to bolt to. With the cylinder mounted and push rod in place move the clutch pedal across the push rod while keeping the push rod on the same plane as the brake one to work out a centre line/ position to put the hole for the push rod to clutch pedal mount ( use a brake pedal bolt which allows rotation) . Drill a suitable size hole for the bolt. Re install the pedal support and mark out the hole on the firewall for the m/c 3 holes -2 bolt hole and centre hole. Drill out these holes and mount the cylinder. I think the bell housing mods have been covered.
In a nut shell you are trying to replicate the brake cylinder/pedal relationship for the clutch pedal and cylinder.
I hope this helps.