i've fitted MC-21 fairing and GP seat unit to my MC-18. you have to make some new brackets from frame to fairing witch i
did with a strip of alluminium from B@Q diy store. bent to shape in a vice then drilled and tapped it out. seat unit was a bit more
tricky as you have to make again new brackets off the sub frame to get it to sit right. it needs to go more forward and lower down. the cost involved once you get ya fairing + seat unit is nothing. just a few quid for the alloy strip. looks mint tho now finished.