Very glad you like them my friend, as I said I am just doing my best self taught on the lathe and its great to know people are happy with my efforts.
You are looking to bore a hole in your pride and joy at just under 22mm
the least nerve wracking way I found to do this was to buy a step drill they are not expensive and as the name suggests you can bore a hole from a few mm up to 50mm in some cases in a series of gradual steps, the resulting hole is also slightly tapered which is great as you can take your time and get the female section of the cap set to fit nice and flush with the surface, by this time the cast in plug will also have just about gone! then simply super glue in place then when set a milliput weld line around and coat of paint and you are ready to go.
Hope this helps and thanks again.
All the best Paul