Thanks!
Well, unfortunately there's not much room between the U-bracket and where it mounts on the engine. We basically have to design it to fit tightly as these guards are designed to fit a stock bike unless we include the washer with the kit thus making it a required modification. Although, it sounds like the gap is on the right for some people and on the left for others. So, I'm not sure how we'd be able to handle that. However, there is quite a bit of room to add a washer (or a few, actually) between the U-bracket and the bracket that's welded onto the guard, if one feels like it (the bracket that's welded to the guard simply gets bolted to that lower hole so you can easily add some washers between the two brackets). Adding a rubber washer to that spot may still reduce vibration a bit.
The washer suggestion is one that appears to have went by the wayside. I'm not a COG member, so I can't currently access David Murrow's article on Debuzzing The Concours. It was one of these tech guides where I found the suggestion of adding the washer between the frame mount and the upper engine mount. Some say it helps, others say it made no difference. In my case, I did a LOT of things incrementally, which together help a fair amount.
Also, I may have my understanding backwards. I just read an article from another site where the writer noted the gap generally being on the left side. I thought it was the right side, and I as I recall at the time I did this (back on '09), my gap was the opposite of what others were reporting.
All in all, it's a minor point at best. Just felt I should mention it at least - if other C-10 owners have thoughts on this I'm sure they will share.
I'm thinking, though, that the added surface area of the tubular guards will give the engine another 'route' to transmit and dissapate vibrations, which may help reduce the handlebar buzz a bit. Also, I figure that if the installer can gently pry the front attachment on your design outward on whichever side you determine has the gap, that would be sufficient for those worried about this. In my case, we are talking a very small amount here (maybe a millimeter or three), and I don't think this gap ever is very big to begin with. Again, other C-10ers can share what they've seen r.e. this potential issue.