What the heck is that

White fuseholder is likely aftermarket, at least never seen in factory wiring. I use the modern type that holds a blade-type fuse. The e-brake switch was in later cars with a dash "Brake" lamp. If it shorts to ground, or another brake sensor does like the pressure-imbalance switch (dual brake plumbing ~1967+), the lamp lights (switches in parallel on low side). Same deal in my 1996 Plymouth, adding a brake reservoir level switch. I added the later e-brake switch to my 1965 Dart, to an under-dash LED lamp, with also a level-switch on my modern master cylinder.

If you don't like that radio, you could mount a modern Android box ("head-unit") which serves for radio, GPS, and many Android apps. I put a low-end one (~$80 + $20 backup camera) on my Dart and Valiant. Sits in front of the dash, using bolts thru the knob holes to secure, but doesn't project much since thin. Seems my processor is too wimpy to run Android Auto (latest must-have), though high-end ones do. It is supposed to run Phone Mirror, which is similar, displaying your phone screen on the Android screen, though haven't tried yet.