Finding Treadle Parts
 

I've come across a treadle machine that the Sandman site has identified as a 15-96. The machine has had a motor added, but still has the spoked balance wheel. The treadle linkage is missing the ball joint arm that links the pedal to the wheel. Are these arms specific to a particular model of cabinet, or are they all the same, or maybe they are adjustable??

Thanks.