Mick, ask Brian the treasurer about internal slave cylinders. We replaced his way back when we (a hand few of the boys) changed the clutch on his C5. Now I know a C5 is much more complicated than a C3, but damm, not my idea of fun.
Have you considered about going for a center force clutch. Much lighter on the foot while still being mechanical. Mind you, you cant clutch start a car with one, as we found out on my mates Trans Am Pontiac. LOL!!
I have seen external slave cylinders fitted on C3's. The chap from Canberra (69MLC) has one on his.
Cam