I've got an aftermarket 1" bore master cylinder, can be used for brakes or clutch, but I bought it with the intention of tweaking the clutch pressure/feel on the Vauxhall conversion I did.
It will fit in the standard pedal box with a little bit of mod work, but is really designed for aftermarket pedal boxes.
It's brand new, I never needed it in the end and stuck with a 0.75" bore cylinder.
THIS is the kit I bought
It was about £60 when I bought it, so I'll call it £50 posted if it's any use to anyone.