It was a challenge, but I think it worked out well.
First of all, if it was my choice, I would have never removed the factory door latches and locks. The ones used on the P15 were ahead of their time and perfectly adequate. And I will never again purchase a vehicle with any portion of the door latch/lock mechanism modified, shaved, or removed.
However, the previous owner had the bear claw latches installed and the outside door lock cylinders removed and a remote door lock system installed, so I had to work with the hand that had been dealt to me, so to speak.
I originally considered re-installing the outside door lock cylinders, since the latches installed on my car do have a provision for locking. I decided against that after I determined that it would have been far too difficult to fabricate the inside linkage necessary to connect the lock cylinder with the latch. Besides that, I still could not devise a method to lock/unlock from the inside using the factory door handles.
Also, the existing remote door lock system was unreliable. After locking myself out of the car, and having to get in by removing the back seat through the trunk I decided on the following: (a) remove and replace the existing remote entry system with one that was reliable; ( devise a method for manually locking/unlocking the doors from the inside; and © fabricating an emergency door lock release system, in case of lock-out.
First I removed the old remote entry system and replaced it with a new setup from Electric-Life. The plungers in this system were much more robust and reliable, so this restored my confidence.
Next, I fabricated a manual lock/unlock button setup, which looks very much like a typical factory setup with the door lock buttons coming up through the window garnish moldings on either side, very similar to the rear door locking setup on four-door P15s.
It was kind of scary drilling holes into the factory garnish moldings, but after much measuring and summoning up of courage I did the deed. I think it came out OK. Another benefit of the door lock buttons is that when you pull up/push down on either one it also unlocks/locks the other door in unison.
Lastly, I fabricated an emergency-release cable which goes through the passenger side door and exits adjacent to the upper door hinge and comes out in the front wheel well. It utilizes a locking cylinder with a key which helps with my peace of mind (I'm no fan of the emergency release cables which merely terminate somewhere under the car and would allow anyone who knows about it to walk up and reach under and unlock the door).
To operate, you insert the key, turn it a quarter turn, and remove the entire cylinder, which is attached to the release cable, and pull on it. After you have unlocked the door, you replace the cylinder in its holder and lock it back into place.
Let me know if you have any questions.