Sorry man. 55's are plentiful, and one reason is they are too narrow and too tall for a decent sump. Most like to use breeder style that have more capacity at lower water levels.
I have a 55 that was a sump for free if anyone wants (needs a baffle replaced as it was cracked to accommodate a skimmer), and I also have a 55 that's empty and clean up for grabs if anyone wants.