Anyone remember the 'Town and Country' horn available on 196x Caddy's and and other large GM products?
Basically four horns at different frequencies.
LOUD like a train!....

I put a set on my car and have another set for my F150 (yet to be installed).
I plan on a second horn switch: the steering wheel will be normal (2 Ford horns) - a second button will be the 'train' mode (2 Fords plus the extra notes)!

I found a set on FleBay.
Easy to add - just physical mounting and some wire (no air lines and stuff).
Look for a seller called: TheShiftShack (btw - no relation).
He gets these horns and refurbishes them.
You'll like (I Like) the results! Plenty loud!