Having been an aficionado of The Exorcist, I, too, was at the first showing of Exorcist II: The Heretic in L.A. at Hollywood's Pacific (formerly BK's Warner) on the Boulevard.
(It's funny, for years I had wrongly remembered it as opening at the Pantages. I think it wasn't until I looked through newspapers.com at some point that I was reminded of the correct location.)
No big crowd at that early showing, as I recall. My friend and I walked out, stupified. Except for a short clip here and there, I don't believe I've seen the thing again.