I just did my horns. 70 Challenger R/T
I learned the following
1. These are date coded, date is stamped near the horn output opening on the side edge.
2. Dual horns used, one "HI" and one "LOW" - Hi is mounted on top, Low on the bottom.
3. Prestolite brand, not Sparton
4. Bracket bolts to the horn and bolts to the fender with "thru holes" (someone sold me a 70 Duster bracket and it ended up not being correct, so watch out for people saying different models fit).
5. Paint semi gloss black. Apply a thin coat as not to cover the numbers stamping or Prestolite embossing.
6. Horns are indexed so the sound opening is pointing downwards.
7. Use the specified horn bolts to mount horns to firewall.
I found this was a fun project......