im sure that was a 965 ( but classed as a 964 just the porsche turbo part numbers start 965)

993 is the last of the aircooled porsche engines, but has a new body style with headlamps angled back is the more noticable difference

996 is after that they changed to water cooled and totally redesigned the cars to bring up to date , then headlamps and indicators are now made one peice instead of mounted in the bumpers

the 997 is the current range,,,,now has similer angled headlamps and bumper mounted indicators again like the 993 style of before so back to more retro looks yet not too much beetle looking

964 was the last of the classic porsche cars that shared the same main body metal panels from when they first made the "911" series, they generally changed cosmetics like bumpers, ect to bring it upto date

911 is a model name just like boxster, caymen, escort, sierra ect

993 is the chassis type such as mk3 mk4 mk5 ect and is part of the actual chassis number

also the turbo versions tend to have wider front and rear fenders/wings though the 996 carrera 4s is non turbo but does have the wider arches as the turbo,,,,,,, not only that but the carrera 4s also has turbo brakes, suspension and all other turbo hardware apart from the engine


hope that helps answer the questions