I wanted to move my top box back two inches to give more space on the seat for two-up. The mounting system that was on the bike when I bought it was already bordering on hokey with one plate screwed to another plate, set up on 3/4 inch risers, then bolted to the grab rails, so I really didn`t want to introduce yet another plate to move it all back. Ended up just cutting a whole new single plate that worked out well. I`m lucky enough to have access to a machine shop, but a similar project could be laid out plenty well with a scribe and square and drilled by hand or with a small drill press.
Original mounting system...
I ordered a set of Givi hardware for the project (E115F Junction Kit) for $11 that included pyramid, two mushrooms, and a handfull of other stuff that I didn`t end up using. AltRider and Motech also offer similar kits but Givi was surprisingly the lowest priced that I found.
This is how the mounting holes in the grab rails are located on my K8 Wee:
They didn`t seem to be very precisely located from the factory, but with the measurements above I was able to get all five m8 bolts to thread through roughly 9mm holes (couldn`t quite do it with holes only big enough for the bolts and no slop room). I think the grab rail holes were just cast, but had already reamed them out and pressed in threaded bushings when I came to that conclusion, so no way to check. Those bushings were just because the nuts under the forwardmost holes were kind of a pain to reach with the rails in place- that part is probably not feasible to do without a lathe, but it`s a little easier to install this way if you happen to have access to one.
The Givi hardware mounted up nicely the first time- either because they are more particular about their dimentions or because the plastic case was more forgiving than the grab rail holes. Locations for mounting hardware:
The two sets of holes can be laid out independently how every you want. In my case, I moved the Monokey stuff back two inches in relation to the grab rails. The mushrooms from other kits (Altrider, Motech, or whatever) should still be 225mm apart, but the pyramid mounting holes might be slightly different- just measure and locate with the face of the pyramid 205mm behind center of the mushroom holes. Although I didn`t want to keep the whole thing 3/4 of an inch above the rails like my original system, they do need at least some washers under a plate due to the sides of the grab rails being raised slightly above the surface where the holes are. I made nylon bushings for that 0.100 (not quite 1/8 inch) thick, and that seems to be about the minimum I could get away with. All in all, my box now sits almost two inches lower than it did to begin with. Hopefully that will help negate any bad handling that comes from being further behind the axle, but I`m not very sensitive to the intricacies of motorcycle handling anyway.
End result, as mounted to my bike...
^^ Pay no mind to those extra eight small holes- they were already in the piece of plate that I had and did not interfere, so I just ignored them!
I did the fancy-pants cut outs along the edges just for looks- a plain rectangular plate would work, rectangle with the corners chopped off would be dandy.
How the whole package looks with set-back top box...