do i raise or lower ride height to get more

hey fellas

got a question. i have a 72 duster 340. in the service manual it refers to a couple bolts on the front lower suspension as "ride height adjustment bolts" for height adjustments. does anyone one know anything about these? are they effective in raising or lowering height any substantial amount or are they talking very small increments? my front end seems to be somewhat lower in the front then some other dusters ive seen. tires/wheels are stock 14 inch. just curios if maybe they are out of adjustment. what do ya think.