For most of the leg parts I used dowels to mount them to the leg. This allowed me to temporarily assemble the legs without having to glue things on. I will eventually glue the parts on and the pins will help align the parts and give the connection some more strength.
To mount the cylinder I started with an MDF block that fit tight into the back opening. Before attaching the block I drilled two holes for the pins. The exact location of the pins isn’t critical since I have an easy way to transfer the location to the leg. With the holes drilled I used epoxy to glue the block into the cylinder.
To transfer the location of the pins to the leg I put temporary dowels into the holes that were just long enough to stick out beyond the block. Next I put a generous drop of black model paint on the end of each dowel and before the paint dried, put the cylinder in position on the leg and then pushed it down to transfer the paint to the leg. This will leave marks where I drilled the holes. Finally I replaced the short temporary dowel with the full length ones.