The 65 and 66 Electrical Assembly manuals call out for a twist-in tab mounted flasher (no bracket, plastic tab part of flasher) to the LH air duct. I have one of this type in my junk box. My Oct 65 build has a bracket and screw so there must have been a running change. It may be the same as the emergency flasher bracket, C1TF-13351-A or C5SZ-13351-A. The 65 emergency flasher bracket was part of the switch assembly.
Jim