If you check at a local fishing supply, sporting goods or Walmart, you will usually find lead weights of many different shapes and forms. There are flat round weights that come in many sizes from 1/2 ounce to up to 4 oz. These make excellent weight additions. Easy to drill a small bolt hole and using 4-40 to 6-32 nuts & bolts from the hardware departments, you can fasten them where-ever you might desire.
In the average model airplane, the ratio of weight distribution is about 1-4 tail-wise and 4-1 nose-wise depending on the moment-arms. One oz. in the tail will compensate for 4 oz. in the nose, if you have a 4 to 1 moment differential.

Actually, I would never pay the slightest attention to plans established CG ranges. In a very sub-sonic convergent airflow realm as a model airplane is, the standard 25% of mean-aerodynamic-chord (MAC) is the only item that concerns me. If I am within 20 to 28% then the machine is OK to fly CG wise. Depending on the machine's use, I may make adjustments thereafter. After flying it a bit I usually end up in the 25 to 30%. A good Pattern machine or 3D flown by an accomplished pilot can well go far aft of 30%, back as far as 45%, but I don't do either of those items so 30% is plenty aft for my flying.

So if you are flying a Big Stick - that is a derivative of the old Ugly Stick design I believe - and being a straight wing-plan, and the chord is 12" (I don't know, just an example) then a CG at 3" back from the LE would be a fine place to start.