Nigel Burbidge
There are also quite a few crib sheets on the Alan Gibson website (under downloads). I have just taken a look and the only Oxford rail conversion is the Adams radial, which has 1/8” axles. I have converted an Oxford N7, which had 2mm axles. Fortunately the wheels were the same size as the J15 and Alan Gibson already produced a conversion pack for the Hornby J15, which also had 2mm axles. I think your first move would be to carefully remove the keeper plate and measure the axle diameter before considering next steps.
Nigel