Givi Topcase Mount for Concours

The Concours has room for a 3rd hard bag, on top behind the passenger, but no original-equipment bag is made for that spot.
     The consensus among COG members is that the Givi hard bags are the case of choice for this location. I already have a set of Givis on my GPZ-1100 and know them to be fine bags: durable, spacious, easy to remove, and waterproof.
     Givi makes a special adaptor plate that replaces the Connie's top luggage plate, and allows a Givi bag to clip in. I installed this plate, to allow me to use either the 36L or 46L bags I already have.
     Installation is easy, and goes like this:

The adaptor is Givi part number E128. It consists of a steel bottom plate, cast aluminum top plate, and a plastic insert. All hardware comes with it (but no tools).
Start by removing the seat.
Loosen the nylon knurled bolt holding the rear plate shell on, and remove the bolt and shell.
Under the rear shell is the original-equipment luggage rack. This has to come off. Pry out the plastic plugs covering the 4 fastening bolts.
Remove the 4 hex bolts with a 6mm hex wrench (not provided).     Store the bolts, plastic rack, and cover in a safe place. You don't need them any more now.
Place the 4 machined aluminum spacers into the holes vacated by the old mounting bolts.
Fasten the lower steel plate to the bike with the provided hex bolts. Each bolt passes through the machined spacer installed in the previous step and into the threaded receptacle that is still fastened to the underside of the bike.      Tighten with a 5mm hex wrench (not supplied).
Pause for a moment and look down 3 steps on this page. Steve B, of Pennsylvania, wrote to say he found it easier to pull the rubber nipples through now, before installing the plate we're about to install. That sounds like good advice, and I'd recommend doing them here. I don't have a photo that corresponds to that, but you can pull them through, as described below, while the plate is still loose.
Now, place the cast aluminum upper plate on the steel lower plate. 4 oblong washers fit into the honeycomb holes in this plate to provide a solid surface for fastening. Put them in the holes that line up with the mounting holes in the steel plate underneath.
Fasten the cast plate to the steel plate by passing the provided hex bolts through the oblong washers and into the threaded holes in the steel plate below. These tighten with a 5mm hex wrench.
Now install the 4 rubber bumper plugs. You place a plug in one of the corner holes, grab the protruding nipple from underneath, and pull it down firmly so it locks into the hole. (See note above about installing these before mounting the plate in place.)
Place the plastic insert into the space in the cast aluminum upper plate.
4 tiny screws hold the insert in place. You need a #1 Phillips driver for these screws.
Put the seat back on and you're done.
Any size of Givi bag will fit this plate.
Here's a 36L bag (normally a pannier on my GPZ).