S3 stands for "Signature Package 3" and is basically "the works"... It appears that they don't list the Signature Packages on their website after they designed it about a year ago, but it's the stroker engine and about every other upgrade that they sell:
Dinan's Signature Package 3:
-13% Underdrive Crankshaft Pulley Kit
-High Flow Middle Racing Exhaust with 4" Resonators
-High Flow Air Mass Meter/Intake Assemblies
-Free Flow Exhaust With Chrome Tips
-High Flow Throttle Bodies
-Racing Straight Pipe Inserts
-High Performance 5.8 Liter V-10 Engine
-Stage 3 Performance Engine Software
-3.91 Limited Slip Differential
-380 x 34mm Dinan/Brembo Replacement Rotor Set - Front
-380 x 28mm Dinan/Brembo Replacement Rotor Set - Rear
-Camber/Caster Plates
-Carbon Fiber Front Strut Tower Brace
-Carbon Fiber Rear Shock Tower Brace
-Dinan/Brembo Replacement Brake Pad Set
-Dinan/Brembo Brakes - Black Calipers With Slotted Rotors
-Front Roll Control System
-Lower Control Arm Monoball Racing Kit
-Dinan Pedal Cover Set
-Stage 3 Suspension System
-Dinan/HRE 19" P40s wheels
Road & Track's review of the Dinan S3 M6: Dinan S3 M6
-b.