73 Duster 318

360 will give more bottom end and mid range torque and will make 370 easier.

318 can make 400 hp no problem with some mods. KB167 pistons are about the cheapest and will yeild at least 9:1,more like 10:1 depending on cc of combustion chamber etc.

Cam should be in the .480 lift range but try to stay under 230 duration for the street.

You dont have to change pistons to get 9.5:1,just the heads.

Magnums or 302 casting heads will do it. Magnums if you cant port and 302's if you can. Oh and RHS heads if you want a more serious head with great potentail. OU812 here sells them