My original c6 speedometer cable
Sw-c9zf-17260-c. Is melted 
Is the c9zz-17260-a. 3 speed / fmx cable the same??
I did a small block C6 swap many years age and just used the FMX cable and driven gear in the C6. Never had a problem with it. That does not mean you will not. Just my experiences.
This came up on our website last week. The Ford MPC list two different numbers for each - and I would expect that if they interchanged Ford would have shown that so that they didn’t have to carry additional inventory at the dealerships (the purpose of the MPCs)
The different mentioned was the length C6 being longer I believe
Not saying you can’t make it fit - we’ve all done those things 
I used the FMX cable when swapped in the C6. It works, but it’s tight.
The different mentioned was the length C6 being longer I believe
The C6 is about 2 inches longer then a FMX, so that may be true. It could be longer. But we have 2 of us who have made it work with no problems. If your concerned about it then by all means find a C6 cable. Nothing like peace of mind in your build.
Looks like I’m on the hunt for a used or concours correct cable…
Mansfield (and probably others) sells the concours reproduction Transmissions Page 2
I used the much cheaper Mustangs Unlimited version, and no one has ever noticed… 