I've got just the answer for you:

https://www.amazon.com/gp/product/B008515U1U/

This kit has an excellent manual regarding how the radio works . The circuit board is laid out in a logical manner that follows the various circuits that make up a radio. It's a very well written manual. Now to add to all that check out this youtube vid series:

https://www.youtube.com/watch?v=b8Ny7XCyxio

The kind gentleman who did this video did a whole series of all aspects of building this kit and he goes into a lot of theory. This kit and the videos will get you going down the radio theory rabbit hole with no trouble at all!

I've built a number of Elenco kits and while their circuits are nothing fancy they are functional to be sure. You can branch off from there. Hope this helps!

Edit: You can download the manual for this radio from Elenco's website.
https://www.elenco.com/wp-content/uploads/2017/10/AMFM-108CK_low-res-2.pdf

It'll show you exactly what you're getting into. The youtube vids go into much greater detail...