While I am sure you want the correct bulbs, upon taking the lenses out, you will find a 33mm will work as well, but it will not 'seat' in the lenses properly, up to you to test and see if it meets your standards, but I had a few festoon style bulbs that were a few mm off and I just slightly modified the metal contacts and no issue. Since the metal contacts on the rear plate just snap the bulb in place, you should have no issues with a smaller bulb.
Be careful, the last 3 XFs I have done plate bulbs on have had severely degraded lenses to the point where when I unscrewed the lense, they would practically fall apart. Since they are so discolored, I replaced them anyway, and boy, what a difference $25 new lenses make
Good luck Howard, give me a shout if you run into any issues.