I have a 29g I used on my 90, bought acrylic and made baffles but did not glue them in place so that it could be modified for specific needs. They can be adjusted as needed to accommodate different skimmers and return pumps. It is not drilled for an external return pump but could be.
The tank is pretty dirty and needs a good cleaning, but the acrylic baffles I am pretty sure I cleaned up, It also has a PVC pipe drilled for a return that I used to put inside a filter sock.
I have been holding on to it, because you never know when it might come in handy. I paid around $80 for the acrylic (that stuff is expensive) so that is the least I would take for the setup.
It might not fit below the 55 you would have to check dimensions and itdepends on the stand but if interested let me know, you could check it out
