That one board in the back of the case likely *is* the radio.
The antenna hooks in via the silver connector on the right. The radio chain is likely processed in the black IC with the red stripe probably meant to obscure the IC identification. I didn't actually look that close. The IC screwed to the back panel is probably the power amp (20W x 4 channels - The chassis connection acts as a heat sink). And the teflon connector left is where DC power comes in and audio signals exit. The front panel likely has an MCU that interprets button pushes and updates the front panel display. It also would likely control the radio IC on the main board.
I find it amusing that they felt the need to maintain the 1/2 DIN form factor when they could have saved money and put the boards back to back into only a 1/4 DINform factor or smaller. Guessing it was too much trouble/not cost effective to change the chassis tooling!
Hmmm... Now I'm wondering if the "old" radio doesn't have a similar power amp that might easily be replaced for a couple bucks. AM reception would be worth the bet... perhaps I should fit quick connectors for the relevant lines for easy swappage. Stay tuned!
* I do not have any direct knowledge of this radio, save that of a buyer... opinions offered here are that of one in the industry and should not be relied upon with any weight greater than any given person begging on the corner of anytown Planet Earth.