Here is a picture of Led Zeppelin approx. 1973-74.
Look closely at JPJ's bass, it's a five string! There were no fivers in productiopn back then. It looks like a Modified Mustang. I thought I was seeing things at first but count the tuners, there's five of them. That had to be the first five string.
It was probably tuned E-A-D-G-B. Here's a pic below.....