If you have done the rear part of your chassis as in the book, with the 2 round tubes RP1 and RP2, you should have 19mm round tube leftovers. I used these to make the bush-tubes of my pedals.
Then I carved the bushes in a Teflon rod (would have been better to turn them with a lathe, but I had no possibilities to do so)
See beginning of this post
on my blog.