Search Jammer Honda 750 frame, looks like that one.
There was another similasr to that but had a gooseneck, sold as a Machine Shop frame, and later as a Santee.
One of the frames back then, was called an Easy Tail.
I found some part a while back from another type, it had about 8 or 10 inch arm with an axle slot and pivot on the other end..that mounted on the frame and there was a housing to mount a spring above it.
A bit hard to explain.. I would sell those bits..