The 88-93 Fox bodies and SN-95's do indeed have different control arm lengths. The SN-95 (and T-bird) uses a 14" arm and the Fox uses a 12.75 (with the exception of the SVO which was 14" and sourced from Lincoln). Those dimensions are from the center of the balljoint to the bushing center-line.
Now, as far as the actual track width is concerned, the 94-95 is 60.1" and the 87-88 width is 57.9". That's a 2.2" difference.
So, if you take the difference in control arm lengths, you'll find that the control arms will make a 2.5" difference. This means that the late Fox K-member control arm mounts are farther outboard compared to the SN-95 K by .3".
So, by running a late Fox K-member and SN-95 control arms, you'll be looking at a track width of 60.4" vs 60.1" stock. I'm running about 60.4" up front but through spindles off a 99. I'm still running SN-95 specs on the K and control arms.
However, as mentioned before, header interference can be a problem, but you might negate this through the use of Fox headers as well. Also, I believe you'll see steering arm interference as well.
My two cents: If the deal is good enough and you don't mind tearing it all apart, just to find it it won't work, go for it. However, speaking from experience, the K-member swap is an involved task and not simply a drop and swap. I'd suggest waiting for a SN-95 K-member to come your way.