If you choose a spin-on filter be aware that a restrictor with about a 1/16" orfice in it will be required to keep the oil pressure up to the rest of the engine. It doesn't really matter if it's in the inlet or outlet, as long as it's there somewhere. Also, choose a spin-on filter with a much finer mesh than the full-flow systems use. Since a bypass filter doesn't have to flow enough oil to keep the bearings lubed, it can do a much better job of filtering the crud out of the oil. I'd suggest looking for a filter from NAPA or WIX that's intended for filtering super-thin hydraulic fluid with as small a "micron" rating as possible.
The "Frantz" brand filter system I used to sell that used a roll of toilet paper as a filter cartridge supposedly trapped particles as small as 2/10 micron. I was a dealer for a canister system that replaced the LuberFiner 750 on big trucks, and the change interval on the filter cartridge was 10,000 miles. We never changed oil- - -just swapped filter elements and topped off the oil level. Some of the engines my customers ran had over 100,000 miles on the oil, and still passed all the tests an independent laboratory ran on the samples we took at every filter change. If you're going to go to the trouble of installing a bypass oil filter, it might as well be as efficient as possible!
Jerry
