Shawano Tank

I was trying to sort/organize a bunch of photos I took on a drive over Marshall Pass back in 2006. When trying to correlate them with older photos, I noticed that the Shawano tank appears to have changed sides of the track at some point.

Early photos show it on the left-hand side for westbounds (Such as in Walter Borneman's "Marshall Pass", p 85, or here, and later photos - right up to abandonment - (Borneman, p 115, or here) show it on the right. When was it relocated? Was it just a case of the old one wearing out and constructing a new one on the opposite side, so as to allow the old one to continue to function until the new one was completed?