The horn rings can be hard to find, they're prone to breakage where the ring meets the "cross bars". If you've got a horn on your radiator bracket, you've probably got the remains of the ring under your cross bar.
I've seen half ring (bottom only) & full ring styles.
The grill "W" turns up fairly regularly on ebay, half the time at ridiculous starting prices so be patient.
When my Aero was a daily driver in the 70's, I had zero issues with the 6v system, even in sub zero midwest temps. I'm rebuilding the car and intend to keep it 6v.
Some guys do like to go with 12v and alternators although I don't know if anyone here has done that with an Aero.