Coincidence - I just did mine. Crosslink to other thread:
Ignition lock housing replacement and re-key
Ordered new lock from dealer, price was same ~$90, had to show title and driver's license to get matching key for VIN. Parts guy agreed that they clamped down on selling VIN-matched keys/locks last Oct or so.
New lock came with matched key. Key tests good in trunk/doors. Not bad for an '83.
Technique was similar, only 123's have a single slot to release the tab. I used a jewelers screwdriver. 46-640 in the 123 FSM. And 1.25 mm means 1.25 or smaller, not 1.5 or "close enough".
Per the FSM, after tightening the cap all the way, I had to unscrew the cap back almost one full turn to engage the locking cylinder. It's snug and flush with the minus-one turn.
The PO was kind enough to re-install the highly secure lock in the pic below. Yes, you eagle eyes may notice that there are no tumblers in that cylinder. I'm bummed that I can't start my car with a screwdriver or pull the key out while it's running anymore.