I have been glad to read this thread because I have been having a similar problem to Garth. In my situation the parts are a Regina 5 speed and a Campagnolo Nuovo Record rear derailleur. When the chain is on the big-big combination the edge of the rear derailleur clips the spokes. It is easy to adjust the derailleur so that it clears the spokes, but then I can't get it into the small chainring-big cog combo. I have set it so that I can use the the small chainring-big cog, and I just don't shift into the big-big combo. It seems that a spacer would solve the problem. It may be a 126mm axle going into a 120mm frame, but how will respacing and redishing affect the relationship between the big cog and the spokes? I suppose that the spokes would be at a more acute angle, pulling away from the hub flange and freewheel, but is that really enough to make a difference?
I should also add that this is one of those Reginas that seem to move when the wheel is spinning. The body is tight on the hub, but the cogs are not always parallel to the rim. I hope that makes sense.
Can't one just use a bottom bracket lockring as a spacer? It fits on the hub. It's made of steel. It has notches for eventual removal.
Marcus Helman
Huntington Woods, MI