I don't recall who made the tank or the sender. They were both Rock Auto parts.
Two gaskets together were too thick to get the locking ring installed. I ended up taking off the locking ring and bending the little locking tabs outward a bit with a pair of vice grips. It was harder to get the ring installed again, but now the ring presses tighter against the tank when locked in place. I filled it back up and don't see any leaks yet. I believe a gasket about 1.5 times as thick as the stock one also would have worked.
You're right about keeping the gasket centered, and the lock ring too. The hardest part of reinstalling the lock ring was keeping the opposite side from popping out when I would hammer one side. The lock ring's outside diameter should be a bit larger, I think. To keep it centered during installation, I cut a few short pieces of small rubber hose and slipped them over the edge of the lock ring, as shown below.
