I'm going to take a wild stab at it.... perhaps this was built from Don Neill's plans? If it really is that old, I do not believe Hostetler had yet produced 33% Gee Bee Z plans, but I could be wrong on that.
93" span is 33% for the Z.
Don Neill's Z was the gold standard many years ago at 33%.
His son has a Facebook page called "Neill's Scale Planes... check it out:
https://www.facebook.com/Neills-Scal...3697131390552/