I have made a small modification to the connecting rod design. I cut the
con-rod as described in the plan but didn't use the nylon or binding to prevent
any twisting of the joint.
I drilled two 6mm holes through the joint and inserted two 6mm dowels through
the holes, securing them in place with PVA glue. This has given me
a strong twist free joint. I came across something similar from my
mate who builds model ships.