You can get 12s or 13s out of a 318, especially in a Duster, you just need to have the right combo of intake, cam, heads, headers, gears, suspension and tires. But, the first thing you should know is that if you decide to go with a 360, you will be able to put ALOT more power out of that than any 318. The good thing is that the 318 and 360 are very similar, so what you could do is buy parts for your 318 that you can swap over if you decide to do a 360 down the road. I am in the process of doing just that to my 73 Swinger. I got a few things to pep up the 318 thats in it for now, but I am building a 360 into a 408 stroker. Some of the parts that I have for the 318 I can, and will use on the 408 when its time to get it in the car. Just some food for thought.