Interesting video. He mentions that he was not able to purchase the magwell from the parts department, but had to contact customer service and sweet talk them into selling him one.
When he briefly shows the literature from Ruger around the 3-minute mark, it indicates that they also make a magwell that accepts AICS magazines. That would be a nice upgrade for a standard Ranch Rifle in .308 as well. I hope if anyone has any luck sourcing these parts you can update this thread. A Ranch Rifle in .308 feeding from AICS magazines sounds about perfect.