It's going to stick out if you've got a square - it'd need to interface with the catch throughout the whole cycle, and the catch is basically also the stock buttplate here. It needs to be an omni-catch because it's also a floating catch, and it's tough to make a floating square PR. Even if you did, you might still need to omni-catch as you can't control the PR rotating in the cylinder if it's floating.
Oh right I forgot that the whole plunger is free to rotate.