A big welcome to the forum BlueCat.
Here are some ideas floating around in my head relative to your situation. As your pond is relatively small, some of them may apply.
My pond is about half the size of yours, was overloaded with LMB. Also had YP persisting. I added 18 BG 3 years ago, 24 GSF 2 years ago. I've been harvesting bass all along, but really cranked it up the last 2 years, removing 106 or 107 in 2015 and another 47 in 2016. I rarely saw or caught a bass late in 2016. I certainly knocked the population way back. And enjoyed every minute of it. I'm certain the sunfish have a chance now. Just today I used my pond rake in the little bit of open water my aerator is keeping open, pulling in 8 GSF fingerlings, many crawfish, and 6 or 7 bullfrog tadpoles. We haven't seen a tadpole in the pond since 2010! BG recruitment now too.
Too many bass is just that-too many bass. I have either 2 or 3 LMB left approaching 20" that I cannot catch. I'll simply shoot them one of the warm summer days when they are hanging around in the shallows.
You certainly could target the cats when they're actively feeding on pellets. Without nesting cover in the pond, you may not be getting catfish recruitment. Your LMB may be eating all the young. Killing the adults any way you can-hook and line, jug fishing, spearing with one of those ice fisherman's pike spears, shotgunning when they're at the surface, several other methods could knock them all out. Your stunted LMB won't necessarily grow to their potential, but their offspring can once the BG numbers recover.
Electroshocking doesn't necessarily result in fish mortality. If your grass carp even let you get close enough to them to be shocked (mine wouldn't hang around any kind of disturbance like a boat), they could be revived and saved.
Sorry about the way long post. Rather than poison everything in a small pond, I prefer to try hardcore management to effect the changes. If you love to spend time fishing using multiple techniques, don't object to pulling out all the stops, and can be ruthlessly patient, I think you could make quite a turnaround to your fish population. Get friends to help.
Sounds like fun to me! Good luck.
Roger
