If you are really careful, a .243 winchester will make a nice
.308-315 hole in a frame. Might have to grind off a little crater wall

True, but the desired hole is .625. If the relationship between bullet
diameter and hole
size holds true, it looks like the tool of choice would probably be the 50
BMG.
Should produce a hole in the .620-.640 range. Use AP rounds if you want
matching
holes on both frame rails.