I am assuming (could be my mistake) that the barrel is already chambered. If so the headspace should be off of the 22 rim and already set. One way that I have indexed barrels is to use 2 ea. 3 ft. long pieces of 1/4 inch square stock (from lowes or home depot). Clamp the receiver/barrel in a vise. I tap the front sight out of the barrel and balance one at the midpoint of the square stock in the dove tail and balance the midpoint of the other on top of the back of the receiver. Step back a few feet and look down the barrel from the bore end. When it is indexed properly, you will only see one piece of square stock.