I got an old B&M Megashifter on Ebay to use on my 700r4. It works well and shifts correctly for use in a 3-speed. The newer megashifters have an easy mod to be used with 4-speed transmissions, but my shifter looks very different from the diagrams, so I can't figure out how to convert it for use with a 4 speed. I posted this in the B&M tech forum with no responses so far.
link to b&m new megashifter instructions w/ diagram
You can see that my shifter is very different (the ratchet appears to be upside down from the diagram)
As you can see it has a final position for use with a 4-speed, but I can't ratchet down to it, but I can pull up the sprung catch you see below and push it there
My best guess is that I needs a different ratcheting gear, but I have no idea if that is corect or where to get one, since B&M doesn't really sell shifter replacement parts.
The shifter's outward appearnce appears to be a megashifter, and it shifts and ratchets like one and uses a b&M cable, but I can't find a part number, so the first question might be is this a meagashifter? But my overarching question is around if anyone has used a similar old shifter and knows how to convert it to 4-speed use?