i think i had the LP, too...bought it at used record store in late 70s for $1.50 or $2.00 (Byrd's records in Tempe, Az).

With a completely different cover that was released in 1970. I picked it up at a discount dept. store in 1975. 66 Crystal Ballroom sounds about right, I believe this one is in the catalog but I could be wrong. I remember one side of the album was Midnight Hour and the other had Stealin' and The Lindy Rag, maybe He was a Friend of Mine, plus a few others. The album was black with a blue skull and some other imagery. Anybody else remember it?

This is one of them albums that were released by semi-legitimate record companies in order to cash in on the growing Grateful Dead popularity. However the date and venue is probably uncertain.