OK .. here's what ya do. Call the AHJ. Have a quiet talk with them. They will either throw you to the dogs or red tag the booth for no engineering. Either way its not your fault. If they pass the paint booth, its their headache. If they make the owner go get engineering its a change order. IF the owner insists you finish its a change order for engineering. Any of these ideas will make you money in the end.
As for attorneys, they are expensive. Do the right thing without malice and the only thing they can prove is you did the right thing. OH yea, buy a shredder and a hold harmless agreement.
As politely as I can say it, and with all due respect, "you guys dont get it"...this is a HICK town...no AHJ.....no red tags....no engineer...no change orders.....it will not be inspected at all.............They will figure it out, and when they produce what I need, I'll hook it up...