Hi there.
If you don't find a premade sump, I'd be willing to help you modify your 55gal. I received a 55gal sump with my 150gal and it had some compartments missing and most panels were not secure so I tore them out and had new ones cut. Of course I did a pretty basic design, but it was not that hard. The hard part is deciding how you want your sump layout to look/perform.
I don't have a pic but I'll try to get one up to show you what I did. You're welcome to come have a look too, if you dare. :fish1: