Tim, thank you SO much. I have looked at the 1951 accessory installation manual - which might or might not be the same as 1953. They go into quite some detail about the dual firewall mounting, but I don't think they mention moving the standard manifold mount. So, now I can see that one horn was a standard Lo with a manifold mount.
BTW, the present horn is an aftermarket klaxon type, mounted on the driver side firewall, which probably would not be correct in any case.
So I have several choices if I want to use the clamshell(s). If my other horm is "Hi" and if I can get proper brackets, I can mount them both on the firewall as per the Chevy book. Or I can try to find a matching "Hi" horn. Or, I can just mount the one "Lo" on the manifold and let it go at that. I don't think I would have figured this out without your help. Appreciate it.
