Thanks to you all for your help. I've decided to buy the book and try Greg's suggestion on using the foam block. I had a look at the Marryat tool at fly a shop and asked about it there. They suggested clipping a V out of the feather end to get rid of the stem and then tying in the cdc wing. I've tied up some cdc sulfer duns to use on a recent trip and the trout liked them!