Just to add to Chris' description: search for "20mm x 20mm x 6mm isolation mounts". It narrows it right down to what you want. Also, you will need to cut the forward right mount to length as it's a blind hole.
Now, there is possibly bad news with this. The original four mounts are quite likely to be corroded in solid to the gearbox. I would soak them in some form of penetrating oil and leave it for a few hours before trying to twist them out.
If the rubber comes off (it probably will
), slot the top with a hacksaw so you can get an impact driver in. Now, apply a
lot of heat and penetrating oil before going in with the impact driver. An alternative to the impact driver is to get a second-cut file and file two relatively parallel edges on each of the buttons. You have a choice at this point; file to a spanner size or grip with a
good pair of molegrips.
If that fails (rinse and repeat
) you'll need to drill the buggers out. You're going to find that you can get at three out of the four without removing the gearbox but you will need to remove the swingarm to clean the swarf out. Three is enough - forget the fourth one.
If you get to the drilling them out stage and you wander off-centre, you can re-tap to 8mm and drill/file the battery tray to match. You cannot drill and tap the forward right blind hole without removing the gearbox.
OTOH, as one set of mine did, they could just pull straight out. The other gearbox fought me all the way to the re-drill and tap stage. B*st*rd.
Put the new ones in with a lot of copaslip.