FYI here's a link to the page on the Matris website for the FK15 kit:
F15K - Matris Dampers
That photo shows the Matris parts (upper) compared to the OEM Showa components.
I got the F15K kit which they say is for the 12/13 NC700 and 14/15 NC750. I suspect this is a "how many different models can we claim it will fit without being an exact replacement" deal as the travel is not a match for the NC or the CTX. Since they all use the same tube/slider what fits one fits all the rest.
CTX - 107 mm travel per manual (I got 110 measured)
NC700 - 137 mm travel per manual
Matris kit - 225 mm less 83 mm OEM top out spring - 142 mm
GSXR 1000 - 120 mm
SV650 - 130 mm
So if you don't want a 5 mm travel increase over an NC700 a spacer needs to be made to go above the top out spring. I made mine to give 120 mm of travel as is typical for GSXRs. I wanted more than stock CTX but I didn't want to raise the bike very much. It will be a solo rider and no luggage bike so I don't need a lot of extra travel for heavy loads.
The kit did have to be shipped from Italy and it was about 6 weeks after placing the order before I got them. I suspect this is the first one that was requested by the US importer, and they probably only bring in small batches of the "popular" kits (like FZ07/09 Yamaha). The spring that was requested was a rate higher than is in the normal spring range and someone goofed when grabbing a spring of that rate without checking to see that the diameter was slightly larger (there's about a .004" interference fit with the tube ID). But now we know there are alternate springs readily available here (Race Tech and Ohlins) so that is not an issue.
Matthew Patton of Forks by Matt (a sideline for him, not his day job) got the kit for me and put in his own design of compression piston and shim stack. He said that all three of the major conversions -- Ohlins, Matris and Andreani, have a problem in his eyes with their compression control. The new piston requires a different weight fluid than that which is shipped with the kit, though the supplied fluid is fine for using in the rebound leg. The standard Matris compression is said to be improved over the damper rods, Matthew's piston is a refinement added to that, but it seemed a very reasonable thing to do since he charged about $50 for parts/labor.
Figure $550-600 by the time the kit hits your doorstep. It gets shipped to Matt to change the piston, and he also adds a few extra circlip grooves to the body to allow more variation in the position of the lower spring perch. Then you'll need to buy an extra liter of fluid per Matthew's recommendation, which is another $10-20.
Matthew would also need to make the spacers for whatever travel is decided on, but I built a spread sheet to make it easy to figure that out when I made mine so that will probably not be a big additional price.
The Matris kit drops in. I was impressed with the nice machining and finish of the Matris parts.
A set of RT Emulators can be bought for about $120 and a set of fork springs (likely to be needed for many people) are another $100, so the cartridge conversion is more expensive. For about $30 you can get some preload adjuster fork caps from China. But the Matris allows external adjustment of damping and preload where the Emulators need to have parts pulled out of the forks for that (and if you want to change rebound you have to change the fluid). You also get a rebound piston/shim stack that can be modified if needed, the Emulators basically do just compression damping. Once you get everything set the way you like you may never touch the adjustments again, but it is certainly convenient when dialing things in to make a change in less than a minute and go out and see if you like it.
Note: my CTX is a long term project and while the conversion parts are installed it is not close to being ready to ride as I'm doing a lot of other things, so I can't at this time give a ride report on the forks or the Ohlins NC-spec rear damper.
Matthew didn't seem too keen on the Andreanis, and I think they may be significantly more expensive than the Matris too.
I wouldn't mind being able to give a ride report but my projects tend to move in bouts of serial mania, with some progress being made until I get depressed from some setback so if I can get the bike back on the road by the end of the year I'll be satisfied. I have a bad tendency of asking myself "how hard could it be?"
I had a CTX pal stop in on Tuesday for lunch. He rode out from Kentucky to have a seat maker (Seth Laam) in NorCal redo his seat and he was on his way back home. He likes his CTX a lot. He had a Computrack shop put an NC-spec single adjuster Ohlins on the back and Emulators on the front of the bike and said it made him like the bike 70-80% more than he already did. I'm looking forward to a similar improvement on mine.
If it wasn't for my need of fork extenders I would try this setup.
Previous: Kawasaki MT1A 75 (small fat tires, auto clutch), CB400 (Hawk), and after a 20+ year hiatus a NC700X
bamamate, I think you could use them with extended tubes. What you'd want to do is make an extender for the bottom (damper rod) section of a similar length to your stanchion extension and then add that length to the spacer you put above the top-out spring. Back in the day 1" extensions, male threads on one end and female on the other, were offered for dirt bikes to get an extra inch of travel. They'd screw on to the bottom of the damper rod, essentially making it 1" longer.
The short/long of it is that yes it's not that big of a deal to modify the overall length of the unit.