Any way you go, it is $$$ or $$$$.
If you are lucky enough to find a used 54/55 Chevrolet truck radio, it will cost $200 if it is junk and it might have the speaker bracket. If you want to get it working and add FM, you'll pay $300-400+ for that work (on top of buying the radio). You'll need a 6v-12v converter, too.
The 12v modern "reproduction" Antique Automobile Radio is about the same price. Or, get a
non-original looking Retro Sound Apache 12v radio and get the functions you want at a little lower cost ($300).
I have a 6v original, adapted to also play 6v FM - it works sometimes.
I have a nicely restored original 6v that is AM only, but it is almost too beautiful to install.
I have one of those original-looking Antique Automobile Radio units and it will eventually be put it in one of my trucks (I saved up my money and bought one on sale). I'll use it with a 6v-12v converter.