you probably already have this, but Ron Anderson has a whole listing of Monogram Speedt Built models that he is reproducing. . These reproductions are as good as the original and include the molded plastic parts like those contained in the original kits. The Long Midget Mustang would be perfect for that little diesel.
Ron's email is
rwanderson@erols.com
Millville, NJ, July 1950 (yes, same meet Bob Hunt attended as a 5-year-old):
I saw a guy enter a Monogram Speedee-Bilt Midget Mustang, painted metallic blue and powered with a K&B .020, in the "Beauty" event (they didn't call it "Scale"; just "Beauty"). As best as I can recall (having been 10 years old at the time) he placed Third behind a Sterling Waco and a Miniature Aircraft kit of the F2G.
A couple of years later I saw the uncle of a neighbor kid successfuly fly a Speedee-Bilt P-40 kit with an OK Cub .049B. (The landing gear collapsed on landing, of course.) Point is, those little Speedee-Bilts WILL fly on lines with a small enough engine. These days, you might try a Cox .020.
Agree on the Ron Anderson reproductions: I have a few of them, and have sold and/or given away a couple of others. They are absolutely fantastic, and well worth the current $30.00 (better check that) price. Contact Ron via e-mail at the address shown above in Keith's post.