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The A engine was designed to suck dirt and keep running for 10's of thousands of miles. The thick babbitt is will allow dirt to embed and not hurt the crank. With todays modern roads the dirt is even less of and issue.
Modern engines use inserts. They fail with dirt the babbitt does not care about. So the modern engines or any with inserts need filters.
Running with dirt is allowed in all the A systems. The original fuel filters catch most anything that would give the carb grief. Then the original carb has a single bolt to drop the bottom in case you have a problem with dirt getting through.
Keep in mind the dirt is not going to be the reason your engine fails. The number one failure of the A engine is a mistake during the build phase.