Upgrade 23.1 -> 26.x

[HomerJ]

We have an install that is running 23.1 (I know, I know...) on an air-gapped network.  I'd like to upgrade it to the latest 26.x
What is the likelyhood exporting the 23.1 config and importing into a 26.x install will work?  It would be a nightmare to replicate all the step release mirrors in between to go from 23.1->23.7->24.1->24.7->...->26.1