I found this file on Thingiverse. It's a Mark V by Treespirit with a Creative Commons license. It looks OK to me, but is there the wrong number of idlers? Are the details off?
Thanks, Charlie, it's good to have another set of eyes look something over.
I don't think I will be using the whole model, or maybe not straight away. I will be using the sides, and other bits, to change an Airfix MkI into a MkV. I was going to do it years ago with Wayne's paper model printed on plapaper and with resin decal rivets, but 3D printing of certain parts has opened up a whole new area.