Just caught up on this thread . My compliments Paul and what a great thing to do with your son!
Just to close the loop, the engine in that "109" in the Erikson collection is indeed an Allison. I knew they ducted the exhausts down to make the set up look like an inverted DB but it's the first pic I've seen of the arrangement.
Also an interesting tidbit on the Mosquito T.III in Paul Allen's collection: when the museum acquired the aircraft, a large chunk of the one piece wing had been missing as it was sawed off to allow the aircraft to be displayed against a wall. A complete new wing was built by Avspecs in NZ for this restoration.
Looking forward to more!