I think I answered my own question. I found a table on the benelliusa site showing the specs for all the Supernova versions. There is a column called "drilled and tapped" and under my version it says "no". So that sort of sucks.
I don't really need the rail on the top. I am just looking for a shell holder on the side. So if anyone has any ideas....
I have seen some saddle mounts that use the pins through the body like this https://www.trinitysupply.com/Benelli-Nova-Shotgun-mount-and-shell-holder-p/1330.htm
but that puts the shell holder on top rather than the side. Other than some Velcro mounted products, I have not found a side mounted shell holder that uses the pin holes.
The only alternative for the Mesa Tactical product would be to either drill and tap mounting holes myself or get a gunsmith to do it.