So last night I got the new rod mount / belt pulley assembly printed and assembled, it seems to work great, the belts are nicely tensioned now and applying further tension is as easy as tensioning a nut, I'm not sure of the long term durability of it but strengthening it shouldn't be too hard if it turns out to be a bit weak for long term usage.

Of course solving one issue reveals another, my mechanism for transferring power from the motor to the belts is a bit sketchy, a lot of it comes from me gluing the short loop belt and thus making the joint rather stiff that again makes it slip over the pulleys when the joint moves across it, having mounted the belt on the middle of the axle has also resulted in it getting a little bit bent and I've come to realize it might not be the sexiest solution, I am going to redo the rod/pulley mount on this end in the same fashion as the other and I am strongly considering designing a gearbox while I'm at it, I don't know if it is better or not but gears are cool.