Greg, I have nothing new to provide, but for anyone here is the link to see both the 20" banjo and the 24" banjo.
oneway.ca
20", #2407, 7.5" tall and 16" long.
24", #2683A, 8.75" tall and 18" long.
The height should be a self-evident comparison to someone's current banjo. The length could be a bit vague in that you'd want to know the full movement distance, perpendicular to the centerline of the bed ways, toward the operator and away, of both your PM banjo and the Oneway banjo. If we knew the travel distances of each of the Oneways, then a real comparison could be made against your PM.
The overall length of any banjo casting can be misleading for this purpose. It's the previously mentioned travel distance each way of the bed centerline, dictated by the banjo cam shaft length and position, and anchoring block, within the banjo casting that we'd want to know. Then whichever aftermarket banjo dimensions and travel specs matches your OEM banjo the closest would be the right choice. I'd assume Oneway has determined these things to guide a buyer to the best choice for a given lathe.