I have Dougs D452 in my 66 Coronet with the taller RB block. The D451 is listed for your 383 motor. They are 1.75" tubes so they probably will be easier to install with no mods.
They will not fit column shifted cars -
http://store.summitracing.com/partdetail...mp;autoview=skuMake PLYMOUTH
Model BELVEDERE
Beginning Year 1963
Ending Year 1970
Engine Type V8
Liter 6.3
CID 383
Engine Size 6.3L/383
Engine Family Mopar big block B
Engine Swap No
Drivetrain RWD
Power Steering Yes
Power Brakes Yes
Air Conditioning Yes
Standard Transmission Column Shift No
Standard Transmission Floor Shift Yes
Automatic Transmission Column Shift No
Automatic Transmission Floor Shift Yes
Application Footnotes: 15 - Fits Mopar mini-starter.
