My SN had some cracked ribs too and I splinted them rather than welding. Your's is a bit more challenging being they're cracked in the center of the bend. At the time I didn't have the ability to use solid rivets so I used ss machine screws and nylocs with plenty of 5200 to seal the deal. The splints are 1/4" AL stock that's 1/2" wide. I figured that the stock would give/flex with the ribs and hull so as to not be so prone to cracking again which is what would happen if they were welded. The AL stock is bedded in marine epoxy and then tightened down.
Clean up the area real well and post some more pics.
Here's what my rib repairs look like and since 2013 the repairs have held up just fine.