Quote by Andrew:
"Once the lugs were cut away, it would be fairly easy to work the backplate down smooth with a file. It takes a bit of time, but patience and an drawfile will turn rough castings into nice smooth pieces of furniture for muzzleloaders. The backplate was likely worked down the same way."

Indeed I think this is what took place. If you will note the stock Pee Wee .020 and also the cast Baby Bee backplates were cast from sort of metal and afterwards 'washed' not plated or anodised with a brass concoction giving it the look of brass but as you may know wears easily to show that gray metal beneath. See the first pic in this post.
The second pic shows a Pee Wee with normal usage and wear over the years.
The last pic shows the modified backplate.

Quote by MJD:
"Maybe that could be the tank from another PeeWee.."

This too is very true and I thought of that as well but in this instance could very well be the original tank for this engine.

Quote by Mr. Cox:
"Funny, there are also the tell tale screwdriver marks on the red tank in front of the absent lugs (!), so it is as concluded a modified backplate... "

Agreed those are the tell tale screwdriver marks on the tank for an engine with lugs but does not provide conclusive evidence. Good eye Mr. Cox!

However it does seem that this backplate has been modified. Most likely due to the fact that one or more lugs were broken. I doubt seriously it was for racing purposes. A Tee Dee .020 could cure that problem really quick!

As for the .020 biplane Cox made in various renditions, to my knowledge all had a completey stock Pee Wee and used the four mounting lugs to mount the engine. I had the Li'l Stinker version. Ther were others including an Art Scholl and Red Baron plus a 50th Anniversery Gold plated one. Could be others as well.

Robert