I found this emergency flasher clip attached to the back of a "spare" '67 gauge cluster I didn't even know I owned. :-) Any chance others have seen this option and might know when and where it was used?
I think that we previously correctly concluded that the "emergency" flasher is located on the dash sub structure, and the "turn signal" flasher is mounted on the back of the IP.
I've been thinking about the location, inconvenient from a replacement perspective. There is a noise level requirement so that the driver can hear it. Locating the flasher unit attached to the IP might have been done so for this reason. It seems odd that the wires were not part of the main cluster harness and was connected separately. Granted, the noise level requirement is active today, and might not have been there in 1967. This is merely speculation.
Regarding the blue plastic bracket, that is interesting. Pictured below is a metal bracket used on the emergency flasher located to dash sub structure. I'm inclined to think that the original design was metal, not plastic.
Also pictured are a couple metal based flashers, and some plastic ones with built in tabs. Based on my observations (consider how little "plastic" was used in 1967 cars compared to today), I'm thinking that the plastic flasher units are all service or aftermarket parts. This is a bit dangerous, and I'm sure that if someone has proof to the contrary we will hear about it
But that's ok. Sometimes it takes a supposition to bring these things out.
I have not found or recall seeing any metal brackets on the turn signal unit on the back of the IP. Given that the rectangular hole is designed to take the plastic tabs so well, that might blow my theory.
The pictures are in the attached PDF.