I have a couple different arbors, both Hudy, and pretty old. One fits the Jaco rears and one is short as described. Perhaps the Hudy universal arbor is the solution. I've heard that the CRC arbor works well also.

Jaco wheels are always a PITA to get on any arbor straight. The wheel design is such that there is no flat area for the nut part of the arbor to ride on. I always have to tighten the nut very carefully and check the concentricity before starting to true; it usually takes a few tries to get it straight