Welcome to PD's Martin
You have obviously researched the old archives to find Bogdystandards Fag-o-Cad paper sketches
As you will read , John apart from a talented Craftsman, was a person of unique personality

and a sense of humour as dry as a parched Australian desert
John passed over to the Big Steam Shop in the sky, probably some 3 years ago after loosig his two loved Dogs, Bandit & Vinnie
So whilst you have nominated a x double size, would this now be 20 x 24 - bore to stroke?, and have the plans been drawn in Metric or Imperial?
I could think of no more fitting courtesy to John, but to post a copy of your take on his engine plans to our archives under the Title of
Bogstandard x 2 EngineLooking forward to your progress here on PD's
Derek