I saw something that mentioned that Led Zeppelin, when first touring the US, opened for Iron Butterfly. I remembered going to an Iron Butterfly concert with Eric S. back in the day. I don't remember much about the opening act, only that Iron Butterfly wasn't all that much better than them. Could it have been Zeppelin? Hello Google.
I didn't find out who was the opening act, but I did find a reference to a show identified as August ??, 1969. I learned this because MP3s of bootlegs are available online. It looks like Zeppelin was elsewhere that August.
Should you want to hear it, you can download In a Godda Da Vita and Theme at
http://www.megaupload.com/?d=8I8T8DZ5 A little bit is missing at the beginning -- I remember that they didn't exactly launch into the tune crisply. The sound quality is pretty much the way I remember the concert -- like a cross between a transistor radio and a lawnmower. There is one spot in the tune where they play a resolve chord and I thought they were going to pull the plug on it. Yup, that is in there. After the concert, I remember Eric complaining about the interminable drum solo. Yeah, like rocks in the dryer - it is there.
It was fun to find but way beneath YouTube.