Here's how I'm planning to address the situation when I build my Cadillac stroker engine. It will have two filter systems, a Frantz bypass filter to actually clean the oil, and a full flow spin-on filter to catch the rocks, marbles, bowling balls, and other big chunks.
My 261 block has the big ports and the dowel pin, which is currently in the bypass flow position. I'm going to drill and tap the plug so I can use a slide hammer to remove it, and then tap the hole for a 9/16" bolt all the way past the oil passageway. I will thread a bolt into the hole until it bottoms out and use some blue Loctite to retain it. There is a very simple way to swage an Allen hex hole into the bolt after cutting the head off so there won't be an ugly bolt head sticking out of the block, in case I ever decide to remove the threaded blockoff plug.
This procedure should ONLY be done with the block stripped down to bare bones so any chips from the threading process can be thoroughly cleaned up.
Jerry
