Assuming the GMC would be the same as a Chevy, the lock mechanism is in the latch, and I don't think you'll find a driver's side latch that has the locking mechanism (whether is would be NOS or aftermarket). At least I haven't seen one. Passenger side would (NOS and aftermarket) cause that's how they came originally.
Provided you added a lock on the driver's side (which I have done on a 51), adding the shaft would do no good as there are no provisions on the latch for the shaft to operate, like it does on the passenger side. But I did some fabricating, on the lock cylinder I bought and to my existing latch, and it functions. All you'll have is the lock face showing under your door handle, with everything else being inside the door. Would be kind of hard to explain what I did and how I did it, but the design is really simple. I think I have some pictures of what the latch looks like after I did my addition to it. I'll see if I can find those.
