Hey i am in the same boat. Have you been able to find anything?
I have been looking into the Octo OS-24A as a suitable option but i am a brand new NOOB to this hobby. I don't know if it's any bigger than the Red Sea upgrade sump but with the dimensions it does sound like a viable option. I only like this sump because it does come with a ATO Reservoir. I wonder if anyone has used it or set it up in this tank.
As far as piping, i think the only actual pipe work that would need to be done would be to cap the emergency drain (since there is only one drain connection) and pipe over the main drain to the left. I have seen some reefers use flexible hosing to connect it without doing too much piping work. As for the return, i do believe the flexible green hose should be long enough to run from the return on the left from the original upgrade sump all the way to the right of the Octo (so really they just switched the drain pipe and return pipe).
Dont know if this helps or just makes it worse. I really hope someone else could weigh in with a more advanced idea/response.
Ya, its hard for me to measure just by picture but if that one doesn't work and you don't care much for additional space in the cabinet then you can also check out OS-30A. I believe there is about 30" clearance between the door hinges and about the same between the wall and power box.
But ya, these are just the ones that i have looked at and would not assume to know anything about setting these up. I am just as much in search of a sumo like you are. Will most likely go with the OS24A as it will still leave some room in the cabinet.