The end is near...

According to Automobile Catalog, 15 seconds for the Duster 340/4 speed.

Detailed specs review of 1971 Plymouth Duster 340 4-speed offered since September 1970 for North America


Using your website provided,

R/T 2dr Coupe
372 Hp, 401 Lb-Ft., 4041 Weight
5.7 sec, 14.2 @ 100

The V6 isn't that far behind.

SE 2dr Coupe
250 Hp, 250 Lb-Ft., 3719 Weight
7.1 sec, 15.4 @ 90

Do NOT look at ET. I can’t say how many times I’ve said and posted this in my what, near 7 decades. ET doesnt mean jack ****.

Look at MPH. Any other comparison isnt valid. I wont get into tires etc.