lower control arm clearance

Dropped the lower control arm and removed the threaded rod and heim assembly. The rod is tapered where it goes through the arm. It looks like the best option is to switch to a 5/8 bolt instead of using the tapered rod. Can I drill the arms tapered hole to 5/8 inch myself (if I'm careful) or do I have to take it to a machine shop? How thick should the washer be that separates the heim from the arm?