Are you absolutely certain you were both at 70mm presentations? According to this article, Star Wars first ran in 35mm in both San Diego and D.C. and was later upgraded to 70mm. The 70mm showings began Dec. 16, 1977 in D.C. and Feb. 10, 1978 in San Diego. So, the May of '77 recording may be 35mm. Do you remember what theaters you were at?
Ah, that is part of a great debate amongst my SD friends, one has challaged the authors facts. However the DC tape (the one I've found) is AFTER the 70mm date.
Did you use any hiss or noise reduction on your digitization?
BrianM