Sierra games are all still under protection, including Space Quest 4. It has now been released on Good Old Games though. You can get it (and Space Quest 5 and 6) on gog.com for a mere $10:
http://www.gog.com/en/gamecard/space_quest_4_5_6
That will have the 315 max score (almost all versions do, your 340 version is much more rare).