So I went to the Slaters website and while the wheels look very well done, none in the 7mm group appeared to have counterweights. Is that something you have to make and apply yourself?
BTW here is a pic of the wheels before removing the crankpins. Note that the tires overhang the centers and not concentrically either.
To add to the aggravation another forum member built a another 0-6-0 10 years ago and found the same problem with the wheels. He was able to contact Stevenson and get replacements. Might want to try that before ordering. That still might not solve the problem with the square holes not matching with the inability to quarter.
Pete