The GS750 was always over-shadowed by its big bro - the GS1000
Suzook had a few years to study & copy Kawasaki and made a great first attempt - even made a decent frame to go with it.
The 750 has a fantastically tough motor - also a better oil pump: these are in demand for the later and bigger Suzooks as they are a higher capacity (due to gear sizes I think?).
Great bikes and still dead cheap - Nothin' cheaper than FREE