Thanks for the write-up and especially the photos. I followed your instructions, and started out with the Dremel. The Dremel took about 20 minutes to cut one side of the square. Next I switched to a grinder with a cutting wheel. Much quicker - about thirty seconds per side. I was VERY careful not to cut too deep. I had a fire extinguisher handy because sparks were flying everywhere. Great deal of good the extinguisher would have done had anything gone wrong - probably I would not have had time to use it. I'm not a safety expert, so I don't know how safe this whole thing was. Sparks flying next to a fuel tank.
I knocked the lock-ring loose with a flat-head screw-driver and a rubber mallet. I don't think it matters much what you hit it with.
The pump assembly in my 2000 Focus SOHC SPI is held down with four flat tabs in the base - rotating the assembly engages the tabs into the bottom of the tank. It's different from any of the pump assemblies that were available at my local parts stores or anywhere online.
To remove the pump assembly, I had to firmly grab it and rotate it counterclockwise. This disengaged the tabs from the bottom of the tank, allowing the pump assembly to be lifted right out.
The assembly itself can be disassembled to access the pump. The assembly is held together by four push-in tabs near the top. Popping them open gives access to the pump inside the assembly.
Neither of the two strainers that came with the new pump would fit inside the assembly. But I was able to pop the old strainer off the old pump with a small flat-head screw-driver. Then I pressed the old strainer onto the new pump.
To put the plate that I cut back in place, I bolted some plumbing strap material across the plate and onto either side with 12x1/2 sheet-metal bolts. I drilled pilot holes with a 1/8 titanium bit.
PS. Another interesting note. Before disconnecting the fuel line from the top of the pump assembly, I disconnected the pump's electrical harness on top then started the engine to de-pressurize the fuel lines. I thought the engine would die after a few seconds. Five minutes later, with no power to the pump, the engine was still running! Go figure.