These are the known mechanical and performance specifications for your 1958-1963 Royal Enfield Constellation.
Basic Specs

Engine
Displacement700cc
Typetwin
Details700cc twin
Max RPM
Compression
Bore/Stroke
Valves/Cylinder
Fueling
Ignition
Exhaust
Lubrication
Cooling
Chassis
Frame Type
Rake
Trail
Front Suspension
Front Travel
Rear Suspension
Rear Travel
Seat
Seat Height
Alt. Seat Height
Total Height
Total Length
Total Width
Ground Clearance
Wheelbase
Dry Weight
Wet Weight
Wheels & Brakes
Front Tire/Tyre
Rear Tire/Tyre
Front Brakes
Front Brake Diameter
Rear Brakes
Rear Brake Diameter
Wheels
Comments
Post-war Production: Originally with 52 bhp with "R" cams and single TT carb for 1958 & 59 and twin carbs for 1960 to 62; Weak bottom end proved unreliable & progressively detuned to 40 bhp to make it more reliable. Unique scissor-action clutch operation. For 1961 & 62 a "bathtub" model with a unique fiberglass rear end was also sold.[7]