Reg Chambers' boiler number system seems a mystery he has taken with him unto eternity.
For I now own the loco holding the last boiler he built, and its certificate identifies it as RC180, built in 2000. That number suggests no date connection, and I would be very surprised if he built 180 boilers over the years, let alone 766!
The loco is a 7.25" g. version of LBSC's Juliet, originally built as a club project – Reg was a member of the society.