Here's my solution:   I cut off the skirt from the bogie using a razorsaw, and removed as much excess plastic as I could from the bogie.   A spacer is glued to the main chassis using 30thou plasticard and the skirt is then fixed to it. A little bit of filler and a large dollop of weathering - these wagons seem to be one large lump of brake dust/track grime - and it'll be disguised.   Tests have it down to about a 15" radius curve.   Cheers, Mick