I just installed a new shoulder vice about 3 weeks ago on my bench. It has 2 guide bars with guide bushings that are inset into the shoulder of the bench. The guide bushings are about 2 3/8" dia. , but have a flat on one side. With that flat, I couldn't drill it out with a forstner bit. I free hand routed the rebate to depth as close as I could get to the layout line, and then finished it off with a carving gouge of approximately the same sweep.
If you don't want to but the bit, you might try the free hand routing, or routing around a button template with the right size guide bushing to give you the required diameter rebate, then chiseling out the center.
I hope you have a better experience with your vise than I did mine. I bought the economy model from Woodcraft. It turned out to be a Chineese made copy of a real vise. What a piece of junk. I had to rework all the holes and the screw just to get it installed. That's what I get for trying to save a little money.