I can draw something up. The pin holes are 3/4" and after the lowest one, you can do them in whatever increment you want. The two lowest holes are arbitrary - they are just bolt holes to keep the extension from rotating. If you do not have a way to make the pin and want one that is greasable, I might be able to make you one after you figure out the rest (it's length will depend upon the thickness of metal you use). What is important is that you drill the 3/4" holes in each plate in the exact same position. I should have added a note that I installed 3/4" bolts for alignment when installing before I tightened down the two lower bolts and the lowest 3/4" bolt. I also added a spacer so I did not pinch the original plates together.
Ken