Here are some links you may find interesting:
A website dedicated to other Yamaha Superaxes: https://www.alston-family.co.uk/
A website dedicated to many Yamaha instruments: https://yamahamusicians.com/forum
A website dedicated to other vintage Yamaha guitars: https://www.yamahaguitars.nl
A website dedicated to Yamaha Super Flighter guitars: no longer active
A website dedicated to the early Yamaha SG guitars: https://screamingyamahas.wordpress.com/
You can download the “Yamaha Guitars And Guitar Amplifiers 1968” brochure from this link (Preservation Sound): https://www.preservationsound.com/?p=1495
Here some youtube links for SA30 SuperAxes:
‘SA30 – 1 ‘ ‘SA30 – 2 ‘ ‘SA30 – 3 ‘
Below a nice SA-30 guitar demo from Mike Dugan…
Below a video showing the ‘crazy’ distortion sounds you can get out of an SA-30 (second half of video)
This song of mine uses a Yamaha SA-70 for the bass line:
Below a modified SA-50 with Rickenbacker pickups