I'm looking to do a wood build for a Benelli M1 super 90 entry. I understand that the Beretta1201 is close, but does anyone know if it is an exact match? I have a wood handguard for the M1S90, but I am looking for something to match or come *really* close.
Also, I know the inertia systems are sensitive to additional weight, but has anyone tried a Trijicon RMR on a rail similar to these? https://scalarworks.com/optic-mounts/bor-rmr/

I imagine you could just use an M1S90 sporting wood stock. There's a couple on eBay. If your looking for a wood pistol grip, I haven't seen one.

When I bought my M1 tactical it had a scope mount on it that was a lot more substantial than the one in the link you show. It was the first thing I took off, so I can't say if it affected cycling.

You can add that rail and sight with no problem

The entire “don't add weight to an inertia operated Benelli” is way overstated. We routinely add 10-12 round mag tube, etc and the guns still run. Stay away from extra light loads (< 1150 fps, < 1 1/8 oz which often will not run many gas or recoil guns) and you'll be fine.