I'll give it a shot. I don't have much experience with them but that looks like a two rail system. The pump slides down the rails and if I'm not mistaken there is a rubber gasket on the pump that in-gauges a fitting the discharge line is connected to. Something like a pit-less fitting in a well. The problem is pulling the pump up. The rails get a build up on them making it very hard if not impossible to pull the pump.
I found a link to the system I think you have. Open the file A-1029-A it's a PDF file showing the two rail system.