Hi Scott,
now gimme one second to answer you ... calm

You can use the build in extension to redirect errors, or ReDJ. In the latter case you have the "Errors" tab, where you can trace any error URL (just enable this feature in the plugin) and redirect to a new URL. This is better of .htaccess file, expecially if you have many URLs.

Another solution (the one I would choose for my site) is to create a table with two columns (e.g. old_id and new_id), and associate any old id with new id. After this I could redirect each old URL to new URL with just a single rule.

After you decided how to proceed, let me know if you need more help.

Kind regards,
Luigi