Like DartGTDan I don't know a ton about the '70's. Both of my GT's are '71's, so that's what I spent my time learning about.
I can tell you my EL5 GT has factory power steering, while the GK6 car was manual. I have the fender tag and build sheet for the EL5 car to prove it.
I can also tell you there isn't a ton of info from the factory about how these cars were equipped, and while Bruce knew a lot about them he was still finding things out about them himself as he added cars to the registry.
I had the pleasure of talking to Bruce a few times by phone about my cars. The GK6 car was #69 in the registry, and the first '71 in the registry with dual mirrors. I forget the registry number of the EL5 car, might have been 65. I have it in my files somewhere along with copies of the registry list from the website.