I'd quite forgotten about valve gear! That complicates the plot a little. AGW do the wheels for a conversion, Dave Franks the coupling rods, I suspect that the RTR connecting rod and Walchaerts can be adapted, perhaps. Looking at the Brassmasters website, I see that the boiler is a resin casting, so the rest is possibly possible, but it costs £165 with the Ultrascale wheel sets getting close to doubling that. I think that if I do this, I'll stick to the cheapskate method!
I too would like to apologise to 'mikemeg' for causing his excellent thread to wander.
Regards