I was surprised to not find hardly any info online about this issue. This was a customers ATV so I ended up just telling him the situation and bought an entire new half. If it were mine, I would have hacked out that rod like you're doing. Be careful securing from the inside. If that clip comes off, could cause carnage. That pin backs up to the ring gear and could slide into the bolts on the back of it and a clip floating around in there wouldn't be so great either. As long as you get it on there SUPER TIGHT, could be the answer. I had thought about grinding it from the outside and pulling the pin out that way then tapping it and using a set screw to secure it back in, I think the 660s are done like that from the factory. I think 2007 with the 700 is when they stopped doing it that way, no idea why. Second choice, having the hole welded closed from the outside after sliding the pin back in. Good luck.