I can't address your question specifically as it relates to Britannia, but I've tried to use ball bearings in a couple of locos, always with no success. I'm sure they would be a great running success, . . IF I could fit them in. Invariably a small ball bearing with an OD which will fit within the limits of a typical axle box, has an ID such that it reduces the axle diameter axle to the point where it can become a weak point and undersized for the wheel. Personally I like to retain as much axle diameter to the back of the wheel as possible.
A solution is to use needle roller bearings and matching hardened inner races. Needle bearings require careful fitting but they can work out quite well as long as their fitting, alignment, and lubrication needs are looked after.
Cheers,
Harry
Edited By GWRdriver on 16/12/2014 03:53:52