Lotsa options...
* A punch is a possibility but try it on scrap first;
* A dremel is a possibility. Maybe you could make a circular template and use that like a router guide. My guess is that you'd want a cutter, not a grinding stone/sandpaper;
* Another possibility is a pneumatic die grinder with a rotary file (more power!), but you might not want to attempt that with instruments still in the panel -- the vibration might be damaging to those other instruments, I don't know;
* The rotary file would be easier to use on the bench than in the airplane, probably true of all the options;
* You could also get a nibbler and use that to enlarge the holes. This one (
http://www.cleavelandtool.com/Adel-N...uctinfo/NTA25/) is probably stout enough. After you nibble, file/grind it all smooth;
* And the last option is to make a false panel with the correct size holes, not worry about how well you open up the existing holes, and attach the false panel to the real panel. If the existing holes don't have mounting screws in the way, this might be an easy way. It would be ugly, but probably your easiest option for nice round holes if the punch doesn't work.
Sounds like way too much fun... :-(
Ed