fuel pump removal

I have a ’99 Mustang and I’m trying to change the fuel pump. I’ve got the tank out of the car, took off the fuel pump access cover revealing the fuel pump and sending unit, but I can’t figure how to get it out of the tank. I don’t see anything holding it in. I’ve tied to pull it out but seams to somehow be stuck (attached) to the bottom of the tank.

This model does not have a retaining ring. when you look thru the access hole you see the fuel pump/sending unit assembly. It's about 4" diameter and kind of the size of a coffee can only it's made out of plastic. I can wiggle it a little, but I can't pull it loose. I looked at the bottom of the tank directly below the assembly and I can see some "spot weld" marks which leads me to think that the assembly is kind of plugged into a metal bracket to hole everything in place. If I pull real hard it might come up, but if not I'd break it and were are talking close to $300.