how to adjust vacuum advance

what i have is 73 duster with 360 and i put in pertronix ignitor ingition and flame thrower coil, i set my plugs at.045 and was told i should adjust my timing to about 34 or 38, i think my timing is only about as high as it would go on timing mark about 10 or 12 i believe, so i was thinking i could adjust light to about 38 and turn dist till i get it on mark, i dont have tape to go by and forget about vacuum advance, does this sound right? thanks