I have a playlist that gives me an hour of live tracks.
I could search all song names for the word "live", but it's not foolproof. I prefer to use the keyword "live" in the comments tag.
Prepare your live music as follows: Create a smart playlist that looks for the word "live" in both song and album titles. Select all the tracks and get info. In the comments field, put the word "live". Click the Okay button. Go through your library looking for any albums you know are live but don't have word "live" in the song or album title. You could use a smart playlist that excludes all songs containing "live" to get a better view. Tag these songs as above.
Change your original smart playlist to look for the keyword "live" in the comments field. Specify an hour's worth and you've got yourself an hour of live versions.