Ike,
Here is the 1967 'H-Code' 383/280 HP 'specs'
* 10.0 -1 Compression Pistons
* Piston Height -.007 (Negative, below deck surface)
* Cylinder Heads Casting #2406516
* Closed-Chamber 73.5 CC
* Intake 2.08" x Exhaust 1.60"
* Valve Springs #134 lbs. (Valve Closed) - #208 lbs. (Valve Open)
* Camshaft (Hydraulic) .425 Intake / .437 Exhaust ~ 256*/260* Duration ~ 32* Overlap
* Carburetor (Plymouth) Carter AFB {525 CFM}
* Manual #4298 ~ 1 7/16" Primary ~ 1 9/16" Secondary ~ (Venturi's 1.186 x 1.313)
* Automatic #4299 ~ 1 7/16" Primary ~ 1 9/16" Secondary ~ (Venturi's 1.186 x 1.313)