Should really be called sweet eight as Julius doubled it up.
Also be aware that the boiler as drawn will not meet most boiler codes so get it checked before buying and cutting metal.
For anyone who wants some guidance on making the engine or would like to do it at the original size which would fit a Unimat or Sherline lathe then the original magazines are available on Model Engineer's website, they start in issue 6.
Also from memory, Rex did not use DP or Module for his gears so they may also need looking at if the drawings are simply doubled
The book is also still available from T publishing