Last time I ran into a similar situation....a phone call to the Mfg. (CH), a field engineer arrived, looked, measured, sketched. 24 hours later I had Eng. signed/sealed drawings, and costs.
Came time to install, Factory Field guys came, fabricated a few extra bends, and made it work.
AHJ at site, looked, took copy of drawings & cert., left Approval sticker & cut-in card.
BTW, the overall $$$ was not that bad, considering what they did, plus the install.
PS: The same services are available from other mfg's, you just have to track down the right contacts.