I tried three different handlebar setups on my CB500 until I picked up a new CB400 set and LOVE them.
The wires fit through pretty easily guys, don't know what you are so worried about? I sprayed a little teflon inside the bars and they went through fine. I used a hook made from thick wire to help a bit but it wasn't a problem at all. OH, I also put another layer of shrink tubing over each wiring group, as there were some cracks in the original, that might have helped in pushing them through, too.
Everything else bolted up with ease, no problems at all. Oh, I had to reroute the cables a bit but I didn't have any other hassles (non-stock master cylinder though). The new bars look and feel great on my bike-a BIG improvement over the mini apehangers that are the stock ones. . .lol. If I recall, didn't European CB550s come with the CB400 bars or some really close to them, too? (not having the chopper craze at that time, like the US did)
I had to drill the wire and pin holes on another set of bars (different type) and it took forever to figure out exactly where to drill them out and it was a pain. It is WELL worth it to just buy the CB400 bars, not having to do your own drilling and have the wires inside the bars.
[img width= height=]http://farm2.static.flickr.com/1223/1197392021_eb80abda38_o.gif[/img]
Honda CB400F bars - part #: 53100-377-000