If you ever had any experience with the old style Hurst shifters from the 60s-70s, you'll remember the "neutral alingment pin" that held the shifter's arms in alignment while you adjusted the rods to the right length to fit in the shift levers on the tranny. The C-5 has a similar adjustment.
I have the shop manual at home, but my computer is at work, so I'm doing this by memory. I did this adjustment to my car several years ago, when I installed my Hurst shifter. Basically, there is a long shaft that controls the shifting action. The shifter moves this shaft fore and aft, as well as rotating the shaft as you go side to side through the gates.
If you remove the shift boot, and possibly the console cover, (I don't remember if the cover has to come off or not), you will see this rod on the left of the transmission tunnel. There should also be a "hitch pin" clipped to the front of the shifter. When the shifter is in neutral, this pin goes through a hole in the shifter, holding it in neutral. Look at the shift rod, and make sure the hole in the clamp is EXACTLY in line with the hole in the shift control rod. Use a drill bit the EXACT size of the hole in the clamp for verification.
If the drill goes through, you're OK. If it doesn't, loosen the bolt on the clamp, and slide the clamp fore or aft, or rotate it, until the drill goes through both holes, verifying alignment. Tighten the bolt, IIRC it's 15 ft./lbs. of torque, remove both the drill and hitch pin, and you should be good to go. Replace the boot and/or console cover.
Hope this helps...........