MrPete222 on youtube does a 2 part video on making this adapter. As stated earlier, the pins are 40 deg apart. The pins are formed in three passes on the rotary table. First pass is done with a 3/16" end mill which gives you a straight pin. To get the 20 deg taper you make 2 passes using a 1/8" endmill. 1st pass the table is shifted .060" in x direction and the rotary table is turned 10 deg, this makes a tapered cut on one side of each pin. For the third pass the table is shifted .060" the neg direction and the table rotated 10 deg in the opposite direction to cut the other side of the pin. The result is a pin tapered to 20 deg. I turned the main body down to 1" and left 1" of extra material so I could mount it in a hex block with a 1" collet. I cut the 3/4" hex with a 1/2" end mill, sorry I didn't take any pictures of that part, and cut the excess material of with the bandsaw. I chucked it in the lathe and faced the end and drilled a 3/8" hole for the 1/2 hex bar that's still to be made.
I finished the main body of the adapter and it does work but it takes a lot of torque to raise the knee.
A 3/8" cordless drill stalled out and my 1/2" hole shooter would do it but you better hang on with 2 hands. I have a 49" table so maybe it's just the extra weight. I also had my 6" vise and 8" rotary table with 6" chuck all mounted on the table so extra weight there. I've never used another knee mill so not sure if this is normal or not but this is how mine is. I will attach a link to the video series and a PDF file of the drawing.
power knee chuck.PDF