I wish I had back all the hours I wasted trying to figure out "The Rain Song" in standard tuning as a kid, until someone told me it was D-G-D-G-C-D. "When the Levee Breaks" is either FCFFCF or CFCCFC with a bottle-neck slide (pardons as my Telecaster is not currently next to me).
Once one has figured out that Page was to "God Of Alternate Tunings" Zep's songs aren't too hard to figure out.
"That's The Way" is so beautiful sounding and easy to play. A standard tuning guitar just does not have that effect. I think half of LZ III is alternate tuning.