It depends because there are three different styles of long boxes for the PS1. I own two of the styles, so I can let you know about those when I get home tonight.
Only one of the styles uses actual inserts in a case. That is the one you have above (which is my scan

). I'm about 99% sure that it will have the same dimensions as a Sega CD or Sega Saturn insert, but I will double check that tonight.
The other two log box styles didn't have inserts. They just had the image printed onto the cardboard or plastic case. The plastic cases were actually pretty nice. I wish that all PS1 games came in those. I have a few of the plastic cases, but I don't own any of the cardboard cases.