I just reread this thread. Some very good points made by all. It seems like the best practice, irreguardless of filters, is to change oil often. This way any junk gets flushed out with the old oil.
Some one was asking about oil filters for the sump plate spin on conversion. I built one and use a filter that fits a garden tractor. You can get them most anywhere a garden tractor is sold. The cheapest I found them is a Lowe's. Around $10, a bit more at Walmart.
I have looked at car filters, none of them are as short as the garden tractor filter.
I have also adapted a right side cover to use an external oil filter. It will also allow the use of an oil cooler.
If I install all the parts the oil flows from the sump through the spin on sump filter to the pump, out to the external filter, to the cooler, then back into the side cover through the side cover filter into the engine. Filtered 3 times and cooled too.
I don't use the spin on sump filter due to cost. The external filter is PH3600 or equivilent.
I can use any filter that has 3/4 x 16 threads for sump or external filter.