It's been done, but there doesn't seem to be a lot of info out there on the process or the specs used. I would use O1/W1 tool steel for the inserts and harden/temper to give some toughness to prevent peening but not so hard as to shatter. Similar hardness to the lifter should do. I would try to remove all the movement of the piston and fit each insert individually until the clip just goes in and seats correctly. No more than a couple thousandanths end clearance.