Dual MATCHED horns RPO or accessory.
I do not think they were High-Low?
We are drifting off topic as the original question only related to the horn mount itself.... but I will entertain the banter.
I have 2 NOS dual horn kits & both have seashell horns in it..... one is stamped H, & one is stamped L.
I assumed that they were different tones but.... I could be wrong.