Drill and tap that dowel, and you can push it in and pull it out at will, but I can't see a good reason to do so. Of the three 261's I've got on hand, only one has the full flow plumbing, and right now it's in the bypass mode. When I build it up, I'll probably set it up for full flow to strain out the rocks, marbles, and bowling balls, and also use a Frantz type toilet paper filter to really clean up the oil in bypass mode. The Cummins 855 cubic inch inline engines used both full flow and bypass filters at the same time, so the concept is at least 60 years old. Wix has bypass type spin-on filters that go down to 1 micron filtration for people who don't like changing a cartridge type filter. A roll of cheap toilet paper gets down way below even that level of filtration. Most full flow filters are at the 10-15 micron level or larger because they have to flow enough volume to keep all the bearings lubricated.
Jerry
