Nigel Burbidge
Bob,
Yes, the B17 had 3mm axles. Sometimes Colin at Alan Gibson can be persuaded to produce wheels with a 2mm centre. I have converted a couple of Hornby J15s and an Oxford N7 to EM using Gibson wheels with 2mm centres (as the RTR models have 2mm axles). My other comments on the valve gear hold good. In addition, you ideally want to go for minimum sideplay tolerance on the front driving axle by inserting washers between the frames and the backs of the wheels. That way you are less likely to have anything fouling.
Nigel