There are a variety of ways to do this in the UI and via actions.

First off you have to decide if you want to copy the library only information such 'play counts' ... because iTunes is not placing that metadata in the files. If you want play counts, ratings, etc. copied the information has to be imported into the files. Either manually by Import from iTunes or automatically by setting up the iTunes preferences to do so.

In the UI it's quite simple. You load two variants of an album and use one of the Actions>Copy Metadata functions. Help can be found for menu items via Help>Quick Reference>Help by Menu. Select Actions and then Copy Metadata. Basically you copy all or some metadata from files at the top of the list to the bottom or vice versa.

Via actions there is the Transfer Metadata statement and others which can be used. If a perfect world if the path of an ALAC is deterministic from an MP3 location you could write an action to run through the batch processor to do it all at once.

The only issue is associating the files. I'm assuming that when you say 'two folders', there are subfolders involved. If there is a way to associate the files, let us know and we can supply a tiny action to do what you want. Either we have to know where to copy from or where to copy to.