A second seat could be fitted under the standard bubble canopy of the P-51D. Only a few aircraft were so converted during WWII. One of them carried General Eisenhower on an inspection flight over the Normandy beachheads.
This aircraft has the core of a real Boomerang, but modified AT-6 wings and an AT-6 rear fuselage. Unfortunately the latter is cleary too long, even from this angle. Note the Donald Duck on a boomerang artwork.