Just thought I'd finish this thread off by updating you all.
I've successfully removed the stripped bolt, drilled the head off and as suggested the rest of the bolt was easily removable as it was only finger tight.
I've now removed and cleaned all the clutch plates, they all seemed to have plenty of meat on them, although I'll need to test properly with a micrometer when I finally get round to buying one.
All back together now with replaced spring bolt and ready to try out tommorrow weather permitting.
Thanks again to everyone for their help and support
