Universal Medalist used an Oberdorfer water pump with two mounting holes on early 5411 engines. The flange of this pump interfered with other fasteners on the engine. A shim was used between the engine and the pump to shift the position of the pump away from the engine and eliminate the interference. The pump, now positioned farther from the engine then required two adapters to lengthen the shaft.

Our new replacement pump is now made with a (nearly) square mounting flange compatible with the fasteners on the engine. To replace the pump, remove both the pump and the shim. The pump  shaft extensions will also not be necessary. Using a new gasket, mount the new pump to the engine using the fasteners that previously held the shim to the engine.

Replacing the early Oberdorfer water pump is easier than it looks.

Assuming the female threads on your pump are 3/8" National Pipe Thread (NPT), the correct part for a replacement pump for a 5411 engine can be located here: #Z2857

In the unusual event your pump has 1/2" threads, choose: #Z2880

So as to what does one do with the shim and shaft extenders? Just add them the your bucket of gear that's never to be used again!  

Thanks to fellow Catalina 30 sailor Greg Galtens for the photos of his water pump retrofit project.