Thanks Bill, that's brilliant - I can rest assured that I don't have a Friday afternoon job. As you say, it does look as if they've modified it from earlier models.
I did look on the Oneway website, but missed the video which, incidentally, seems to give all their trade secrets away!
In case anyone else is thinking of making a similar change to their lathe, it really is much nicer to use than the Jet original, but is taller, and the original Jet toolrests sit well above centre. Not a problem for me as I already have other toolrests but it's something to check if going down that route.
The only other possible issue I can think of is that, if using the bed extension on it's lower mounting points to turn larger diameters, the Oneway banjo is about 16" long, sized to suit a 20" lathe swing whereas the Jet is quite a bit longer - almost as if it was designed for their bigger 24" lathe and the height cut down to suit the 3520. A 12" toolrest (6" either side of centre) would barely cover the diameter (38"?) possible when using the bed extension on it's lower mountings but a 14" or asymmetric toolrest would be fine for 38" diameter.
The much improved clamping means that longer toolrests are far less likely to turn in the banjo when being used close to their ends.
Now I'm going out to the workshop to use it!
Duncan