I can't seem to post a reply on John's thread, so apologies for posting independently.
Jessie plans etc are with Reeves. If you want to see good drawings look no further. They are quite beautiful - every part is clear to see, every last nut and bush is shown - just fantastic.
Wilfrid Underwood
Jessie was not described, but its big sister Bridget is - in Model Engineer from 2 January 1970. Ken Swan explains how he conceived of the engine as an 040, and built the chassis in this form, before extending it to an 042 to make Bridget. He incudes a comment that the engine would look handsome as a saddle-tank 040 with inclined cylinders, so that seems to be the beginnings of the Jessie version.
Wilf
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