If I'm not mistaken the one that holds the speedo gear on the output shaft is the same, if not take the cluster to Westlake or a place that has the round balls and try fit.
I measured the speedometer ball hole and the one on the cluster. They are the same size. The ball from the speedometer measured 6.35mm. So basically 1/4". Looks like sling shot steel shot will work or bicycle ball bearing.