There were 2 model airplanes under his house? You mean like in a crawl space?

OK, well...

Your best bet in getting this stuff working would probably to talk with someone in a local club or at a local hobby shop. Don't sell anything until you get a couple estimates on what it's all worth. They might be computer radios, or antiques, etc.

As for putting the OS .40 in a Cox foam plane, I don't think that would work too well. That size engine is not going to fit very well, and if you did make it fit it would make the plane extremely nose-heavy. And if you added weight to the tail to balance it, it would probably be too heavy to get off the ground. And if it did get off the ground the power of the .40 would probably pull the foam wings off. I think you would be better off to get one (or both) of the planes you found working again.

Of course, I could be wrong about the Cox plane. They are usually very underpowered.

All in all, sounds like a lucky find!