There are all sorts of attachment surfaces inside an E-Series but your current build-out might affect how accessible they might be.
There are body builder layout manuals showing the inner structure which might be helpful. If you have access to a cargo-only E-Series without any build-out you can compare---they're all the same from 1992 to EOL in 2013.
I might have a few photos but nothing comprehensive, the proverbial before & after sorts that is.
HTH
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