Mike the secondary filter which is the one on the top front of the engine is kind of limited in what is available. If you do an interchange search with the factory number you get the factory spec which I believe is the 3260 which is 10 micron.
The Racor is an accessory unit sold big time in the marine industry. It is a primary filter to keep the trash and water from reaching the secondary filter and the injector pump. It is a relatively small filter that fills up fast. Like boats chances are old moho's have nasty stuff in the tank. The more pre-filters, the more stuff removed saving the final filter.
I installed a large spin on truck filter about 3.5" x 8" where the Racor used to live. I moved the Racor on top of the frame rail where it is easy to reach. The large filter is 21 micron, the Racor is 10 micron and I haven't changed the filter on the engine in ages because it only sees clean fuel. I just find changing my pre-filters easier than dealing with the beast on the front of the engine.
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