I tried this ages ago with my '18 and wrecked brand new a seat unit so take care!

Part of the root of the problem you've got is the mc18 subframe is too high if you want to run a foam seat pad as the o.e. seat unit sits lower than the top of the subframe and the seat pad itself then sits higher.
Remember on the road bike the seat pad sits on the subframe and the bodywork just sits around it slightly lower effectively doing nothing.
Looking at the Tyga MC18 "GP style" seat unit and a real GP seat unit you can see the issue all to clearly. Fit the GP seat unit onto the road sub frame and the seat is always going to be too high by quite a bit.

I think you might find that it's impossible to retain the stock subframe, use a "race" seat and get everything in line. To get it looking right you may either need a new subframe or some very careful cutting to let you run the o.e. seat pad.

I'm not suggesting you do so, but imagine if you cut out the section of the seat unit you've got that's covered in foam. It could then sit a lot more correctly.

It's worth anyone with a mc21 or mc28 who wants to try this noting that the early fairings are far too narrow. You can't get the seat unit on at all (fuel tank is too wide) and the front bodywork is even worse.
The later ones fit quite well and the easy fix for the seat problem is a Tyga subframe and a couple of L shape brackets for the mounts.
Though I'm not really a big fan of that shape any more, which is odd, I used to really like it. I think I'll go back to stock shape for the 2013 season.
or just stick with the RVF
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