Just curious - did you ever find out what that chunk-o-metal that was found in your oil pan was from???
I think the concerns outlined here are that you have potentially other parts of the timing system which do show wear (as seen in the pics you provided and based on your comments) and that these worn parts could fail sonner or later. If those parts do fail, even after others have pointed out that possibility, a failure as such will only cause more damages & $$$$ than if those parts were just replaced during the time you had the engine open. I think another reason for concern too is that chunk-o-metal in your oil pan, which is not good by any means.
What it comes down to is there is a 50/50 chance the "band aid" fix works now, but for how long no one really knows.
IMO - I would want to fix any potential problems before they evolved into possibly more expensive repairs and a car that is rendered useless due to a blown engine. Plus, spending the $$$ on M42 parts to prevent such a failure is a lot less expensive than doing an M50 swap, especially if you are on a limited budget to begin with...
