Should have realized that would be in the way (was looking at Harold46 picture with extended bracket).
Further thinking (may have strained some brain cells) came up with what is drawn in attached picture.
Maybe a possible solution, although the length of the all-thread rod may be longer than you need.
Also, if all-thread contacts the filter bracket u-bolt, you could just file down that short section of threaded rod to provide clearance.
Good luck on getting your horn mounted and functioning.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)