In the end, I took my clutch and flywheel back to my clutch mechanic an hour's drive away and he is setting it up for me again. The clutch pads are slightly thicker than 1/8 inch each side of the plate but he thinks that won't be an issue.
I actually wonder if the problem was that the clutch was installed (by me) about 2 years ago and has been engaged since (while I concentrated on other things), thereby making the clutch pads stick to the flywheel. In my ignorance, I adjusted the bolts on the 3 clutch levers and stuffed up the settings.
Here's hoping that the whole thing will work properly when I reinstall it again