1968 chargers are not lightweights so your going to need a really good set of heads to meet your goals
I would probally choose a set of 440-1 heads CNC ported and a good, M.W. size intake port manifold like the 440-2 or the 440-3. Hood clearance is probally going to be a issue so maybe to go that fast you may need a fibreglas hood with a Hemi or six pak scoop
Let us know what you decide, BTW my 3450 lb street car runs low tens on Oregon pump gas with the exhaust on and air cleaner in place, so it is doable
Good luck