Well, you're right, Gordon.
They are the full-width bearings, as supplied with the kit and I happily assembled the whole thing 'as per the instructions'.
I may even have some of his slimmer bearings somewhere, but once the hornblocks were soldered on and with the presence of the springs, it's not possible to change them.
If I'd known about this prior to soldering in the hornblocks, I'd certainly have filed the full-width bearings down sufficiently, if I hadn't been able to access any of the slimmer ones.