If you can't find the Folbot instructions, then one of the books by Percy Blandford ought to help. Try Canoes and Canoeing, if you can find it in your local library or second hand.
Alternatively, you could go on SongofthePaddle.co.uk and search or ask there. I know there are a number of people who have recanvassed canoes there, including Percy Blandford-style skin on frame kayaks.
Good luck. And don't forget to take lots of pictures and write up a blog, so those coming after you can see how it is done!