I also have a Wilesco D-22, only mine is a complete Wilesco steam plant. I do love the twin cylinder engines as being generally self-starting and having a much more even power curve through the entire revolution, they just seem especially "RIGHT" to my mind! Using a Jensen #20 boiler to power your stand alone engine seems like a really good idea to ensure that there is plenty of steam available!
Wonderful link-up you have going there!!!