Drilling the piston for the ring locating pin .0625" , 300 degrees from the front of the piston. This will allow it to line up with one of the lands between uniflow ports:
And turning a locating pin using a stainless steel cap screw as raw stock.... for an interference fit:
And pressed it into the piston. The bury was .125, and the stick out was .030", which is the depth of the horizontal leg of the L shaped ring, flush with the inside of the upright leg. The upper part of the piston is relieved above (to the left in the photo) the ring groove to accommodate the outer part of the ring. The piston will be parted off .067" above the ring groove.