Additionally to Paul's suggestion, Windrider makes a pre-fab motor mount with mounting plate and matching backplate for pusher configuration.
here is the web link -> http://www.windrider.com.hk/product.asp?id=188
unfortunately i just started reading this build blog.... and it cost me some $$'s for a new MS flying wing kit..... that said i get to do the happy dance again when the big brown truck comes with a new box.
This model will be perfect
for the moderate winds and semi-rough ground at a local slope soaring flying site in riverside, ca. As a bonus, Gary G. shouldn't be able to knock me out of the sky with his combat wings