How much HP and what do you think it will run.

As for what it will run, depends on how serious and well set-up your Duster is, gearing, trans, converter, and traction wise.
I've driven a friend's car, a very well set-up 67 GTX, with quite a bit less motor and more weight, to 10.60s. If yours is set up as well....... 10.25
Typical street car traction, converter and gearing? Low elevens.