There is a lot of ways to go 9s in a Duster, but you asked for the best. Hands down, 572 pump gas Hemi. Red line it at 6800 and it will live forever, cheap to operate, huge resale value compared to anything else. And the whole range of 9's is available, from 9.000 on up. There really is not reason NOT to go with a Hemi.
Well cost is one of them... Depends on what the budget is. Most parts cost the same, but valvetrain, heads, intakes, all cost more. Then there is the fitment issue of a Gen2 HEMI in a A body. Not denying the cool factor, but there are SOME drawbacks.
