'Tis Lon. ;-)

A more careful reading of the construction notes says
that the Audax driver used is discontinued and so is not in
the PE catalogue.

The Goldwood 8" FR PE part number 290-379 is _again_
out of stock but would perhaps model well for the
Voigt pipe. Since this driver is selling out on a regular
basis I'm thinking that the driver is being used for
current projects since it became available about half a year
ago.

Followup remarks did say that making a Voigt Pipe
includes a fair bit of luck. Terry Cain has also made
this design.