Removing steering coupler assembly to replace rag joint

[Praxiss454]

Hi all,
I have a '65 GMC 1000 with manual steering. I'm swapping out a worn out manual steering box for another I picked up. At the same time, I want to replace the 52 yr old rag joint. I picked up the Dorman Help! 31000 kit, which looks to be the right replacement. I've unbolted the steering box from the frame and dropped it out. Now I'm looking at the steering coupler assembly but I don't see how to get it opened so I can replace the rag joint. Some videos and images I've seen show the coupler assembly held on with bolts and nuts, but it looks like my coupler is riveted.

What is the recommended way to remove the coupler so that I can replace the rag joint itself? I don't have an angle grinder to grind the rivets down, but I do have a dremel with some cutoff disks. Another thought was to try to drill them out, but I've never done that before and don't really know what I'd be doing.

Any suggestions (with sufficient detail, imagine you were explaining it to someone who's never done this before) would be very appreciated.