The only way I know how to do any crossover is with a 126mm spaced rear wheel. I have a 120mm Richard Sachs that was spaced to 126mm, and I run Current Campagnolo Ergo 10 equipment on this. I replaced the rear (right) Ergo shifter cog with a 8 speed cog, and replaced the 10 speed chain, chainring and rear pulleys all with 9 speed stuff. I run a SRAM 9speed chain, any one will do. I have 126mm spaced rear Shimano Hubs, all with 7 speed HG cassettes. They have the same spacing and cog thickness as Camapgnolo 8, so it works perfectly, except you have one extra shift in your lever, but the rear derailleur's limit screws prevent any overshift into the spokes or chainstay. I don't think you can do this with 120mm, unless you run a 5 speed Shimano setup in back, and I don't know if the spacing is the same. You can't retrofit any modern (130mm) Campagnolo hubs. It's not just a matter of spacers, but the width of the freehub body, and you can't do much about that.
Hope this helps.