I'm in the process of building one right now - in essence, a "social distancing" project using pieces/parts/scraps on hand, in some cases going on 50 years (the halfstock blank was from Dixie back in the mid '70s). The under rib is from a scrap of mahogany. I figured with all the furniture making in New England that would not be an uncommon wood. I've pinned the rib and the ramrod pipes to the same tennons - basically securing the pipes to the barrel as opposed to just a skinny piece of wood and also the pipes help secure the rib to the barrel. I also cut a dovetail/tennon shape into the rear end of the rib and then cast the forend tip around that so that when the barrel is in the stock the back end of the rib is further secured in place. I may put a screw in the very muzzle end of the rib - or maybe not. I'll wait and see how secure everything is when it is done. The project is currently on hold for a bit - I had shoulder surgery this past Monday. It's basically done except for the refinements - barrel pin escutcheons, capbox, etc - and I still have to make the sights. This build is outside my norm - it's halfstock and percussion - but it's been an opportunity to innovate and try new things. I'll try and post pics when I'm done.
Stay healthy!
Eric