Used out-of-state vehicles which are Federal (49-State) emissions certified may be registered in California after passing a California emissions test.
As long as this Nissan 240sx has not had its emission systems tampered with (no smog components have been removed or modified) and its emissions fall below California's emission cutscores, it can be smogged and registered in California. Visit the following website to look up the cutscore limits in California for a 1995 Nissan 240sx. You may obtain an emissions test in your state (will not be valid in Caifornia) for the simply purpose of comparing emission results from California to Out-of-State. HC, CO and NO will be measured in California.
The transmission swap should not pose a smog problem since the vehicle is equipped with an OBD-I computer (as opposed to an OBD-II) and no transmission sensors/monitors effect engine emissions. We must however recommend you contact a CA smog check referee's office for final word prior to bringing this Nissan 240sx to California. You may contact the Referee's Office by calling (800) 622-7733.
