Help on how to replace upper control arm mounts

First time poster here. My upper mounts are both riddled with rust. The frame channel looks ok from the outside. I bought the upper mount repos from Classic Industries and am looking for any pointers on getting the old ones out of the channel. My initial plan is to scribe their position, drill out the weld at the top, and ask you guys how is the best way to get them out especially inside the channel. I would sure appreciate any help from those who have done this before.