Attached are some more photographs showing a full-flow filter on a 1954 261, along with a stock 1954 261. Along with the the images that Curt B made available, lots of filter options for a 261 (or 235) show up on this thread.
stock 1954 261 1954 261 with full-flow There are also images of a couple of 1959-62 261s with the factory full-flow filters. On these, you can see the "pin" in the "in" position. There is a subtle difference between the two late model 261s, as one has the 1/8" NPT plug (same as Tom_Dobson's) for the bypass return, but the other does not have the tapped hole in the block.
Late 261 Late 261 details Another late 261, no 1/8" return There are lots of subtle differences between the different 261 models. Also, the casting numbers are not always positive identification. One of my 1954 261 blocks (#3733950) is shown as a 1955-57 in some lists and as 1954-first 1955 (which it is) in others. The other 1954 261 block (#3835911) is shown as a 235 in all casting number lists that I have seen.
