My 421 is 3/4 filled and dry decked, no oil cooler but I have a remote filter (no bypass valve in it,I want all the oil filtered,all of the time), -12 fittings threaded into the block and -12 braided line to the remote filter which is positioned about 18" from the block. I change my oil and filter just once a year, drag use only at the moment. The filter is a Fram PH4825,or occasionally the Champion equivalent,though I've noticed that the oil entry holes in the Fram filter are slightly larger than the Champion so prefer the Fram.
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