MOst of the early redlines, shell and C&J frames used the trackmaster Glass. Heck even the Starracers are the same. So they all have the same rear seat section and single tube under tank, so there 4 frames that all looked similar at the top from that early period, as most guys worked around cal with trackmaster or champion, early in the peice, so they would have picked up the same ideas until they got doing there own designs going. PRobally easier to say what its not. ( champion or trackmaster )
Someone should be able to pick it from the lower sections where the swingarm gussets are and the down tubes sections off the backbone. I doubt its ealier than 74. You may also never no 100% as Any welding type shop could have made it back in the day and the buyer plated it.
So you can only go by 1. someone who actually made it or 2. by someone that actually bought one like this BITD. I'm still not sure of that rear arm and champion style engine Shoe is right - but if it is, then that is unique enough to lead you to its maker.
Redline
C&J 350Xl
Starracer
shell
Cheney