I installed the under cabinet sump in my 260 3-weeks ago. I would love to help you, but unfortunately I'm in Michigan.
I believe you should intimately know and understand how the system works if you're going to live with it day in and day out. If something goes awry, breaks or is leaking you may not be able to get anyone to help you quickly. Saying that, this sump has been a bit of a headache for me. Installing and set up was easy but I've had issues getting the sump level to stay consistent. Just yesterday I was able to remove the Red Sea sump intake valve and replace with a Spears gate valve and this has helped but I'm not quite there yet.
If you don't want to tackle the sump install on your own, maybe replace the rear sump skimmer. I have a used red sea skimmer I could help you out with. Or, better yet IMO, install a HOB skimmer. I removed the original Red Sea skimmer and hung on a Reef Octopus Classic 2000 skimmer. I put this on the back of the Red Sea sump. It fit perfect and did what I thought was a much better job removing gunk from the tank then the red sea skimmer did. I also installed a RO Classic 1000 HOB skimmer on my Red Sea 170. BTW, I'm about to install a under cabinet sump in that tank too.
FWIW On the 260 I used a Reef Octopus Varios 4 pump for return and a Reef Octopus Essence 130 for skimmer and am happy with both of those choices. They fit in perfect and both are quiet and functioning as good as I could have expected.