The final configuration is diagrammed above. I don't remember specifically what I used for C-15, but I'm not gonna pull the chassis again to find out. This is what I ended up with after a lot of experimenting. Here's a link to a 13-second audio sample:
https://flic.kr/p/23F6oQ6
I think that's fairly good for a budget radio with a 4-inch speaker.
Thanks again. It's a nice-looking set and it'll be great for listening to the ball game, but maybe not so good for Toscanini. More importantly, it makes me happy.