Be careful with the push-pull. It has to be set-up just as perfectly as a pullpull, if not moreso. If you have a pull pull, that goes slack, no huge issue. If you have a pushpull that goes slack, that means it's trying to stretch one rod, and squish the other. My advice for pull-pull is this:
Do a full scale mock-up of your set-up, and then adjust the arm length in small increments until you get a no-slop, no binding system. Then, make your own arms and you are done!

Peter