In desparate need of early model 71 dart fuel cap

The difference is EEC ( Charcoal Canister ) vs. non-EEC .

One style is vented ( non-EEC ) , the other is non-vented ( EEC ; closed system ) .

NOT all Ca. cars got the EEC setup in 1970 .
A fellow I worked with had -- and hopefully still has -- an all-original 1970 Swinger 340 , original Ca. model , untouched engine compartment ; he bought it new in Spring 1970 from the local Dodge dealership.
NO EEC setup ; and , it had a chrome fuel cap .
Also , non-thermostatic air cleaner !

Opposite end of the 1970 model spectrum :
1970 'Cuda 340 ( BS23H0E ) .
Built in the L.A. ( Commerce ) plant in late 1969 , for Ca consumption .

Had the EEC setup ; was also sans N42 exhaust tips ( Noise Reduction Pkg , required in certain counties in Ca. ) .

I believe that -- at least when it comes to "B" & "E" bodies , as well as certain "A" Bodies -- it came down to :

- N95 ( Cleaner Air Pkg / Calif Emissions Pkg )
- Motor
- Whether or not the car had an N96 ( Fresh Air Intake , et al. ) hood

I've noticed throughout the years that certain motors didn't get the EEC setup :

- 440 3X2 ( Six Pack / Six Barrel )
- Hemi
- 340 3X2 ( 1970 T/A motor )

-OR-

340 / 383 / 440 single four barrel induction if the Ram Charger ( et al. ) hood , Shaker hood , or any other F.A.I. hood ( scoops on 1970 & 1971 340 Dart / Duster / Demon ) was ordered ( standard in some cases ) .

When the cap has a double-step 'screw' setup ( takes two turns to release the cap from its rest ) , it also has EEC ; these are the non-vented caps ( closed system ).
If there's only one-twist to release the cap , it's a vented ( non-EEC ) cap .

I hope this is of some help ...