While based on the original Gulfstream I, the Gulfstream II (or G-II) shares the same forward fuselage and cross section, but there are more differences than similarities between the two aircraft.
The most obvious difference is the two rear mounted Spey axial flow turbojet engines, others include a new swept wing and tail.

Aircraft Information

 Passenger Capacity: 14
Airspeed (mph): 505
Cabin Width: 7.3
Cabin Length (ft): 39.3
Lavatory Style: Full
Cabin Height (ft): 6.1
Baggage Capacity: 157 ft3