I've been reading your articles on your Beyer Peacock build - very useful thanks, and I noted with interest that you used Gibson wheels.
Any reason behind that, personal preference or were they supplied in your kit? Mine came with Romfords and I've got a slight issue in that once they are fitted and the screw tightened to the axle they bind against the axle bearings. This is my debut with Romford wheels so I'm not sure if this usual with them. I'd quite like to rule out bad chassis building (but you never do know do you?!) as the spacers were inserted with the tabs fully home and its been built square.
Next stop is to check the bearings are secured fully home (I suspect they are as I've got a slight OCD over leaving burrs). Then get the rulers out to check back-to-back readings. If all else fails then the only option I can see is to file the width of the outside of the bearing down slightly.
The Gibson wheels were forced on me at the time due to a problem with the supply of Romfords at the time. This has now been resolved and in future I'll be using Romfords. They are much easier to fit as they can be removed and replaced as often as required. That said, there is nothing wrong with Gibsons, it's a personal preference.
The bearing problem has a simple solution - file the faces of the bearing until the wheels fit. I've done this until the "brim" bit of the top hat is little more than a smear of brass on the chassis side. I suspect that this is a deliberate move on behalf of the chassis maker as it allows the builder to have as little sideplay as he or she wishes. Other makers require you to pack out the wheels with washers to achieve the same result.
One of the beauties of the Romford wheel is that it is self gauging - once the retaining screw is fully done up, no further work is required. In fact no further work is possible unless you want to re-manufacturer the axle and if you do, you need more help than I can provide.