Hello Roger,
A Minisail N°4 submerged on Ebay in 2012. The boat was then in the Edinburgh area and the builder plate indicated a Plycraft built.
I have only one screenshot from back then to be found here: (scroll way down the page).
The daggerboard slot being positioned in the foreward end of the hull is an indication of a very early make. Not sure though if that was "Dumbo", if I remember well there was no name visible on the boat.
Who bought it or what happened with since then it is not known to me. At least any new owner has not contacted the Minisail C.A.
Why not try and ask on the CVRDA forum?
Greetings,
Ronny