Brass is about 5% heavier than steel. A brass weight bolt might get you close if you can find or make one.
The OP wants to add 0.6 oz. Changing from a steel pin to a brass pin of the same type will probably add only one or two tenths of an ounce.
As a player who has fiddled around quite a bit with cues' weights, I'll list some alternatives for increasing a cue's weight:
• Change to a heavier shaft.
• Add weight to the existing shaft (e.g., install metal above the hole for the joint pin).
• Change to a heavier joint pin or combination of joint pin and brass shaft insert.
• Change to a heavier joint collar.
• Add weight below the joint pin (e.g., install metal, or core the forearm with a heavier wood).
• If it is a wrapped cue, add weight under the wrap (e.g., install metal in some fashion).
• Replace the handle with one that is heavier.
• If the current weight bolt is lighter than steel, change to a heavier bolt.
• Lengthen the current weight-bolt hole and use a longer weight bolt of the same type.
• Change to a larger-diameter weight bolt.
• Change to a weight bolt that is both longer and of larger diameter.
• Do some combination of these alternatives.
Note that some of these alternatives would be expensive (perhaps unwarrantedly so) and/or affect the cue's balance (which might be good or bad).
[And some cue makers and cue repairmen probably would not do some of these alterations.]
Edit: And I note that the OP was asking about an Ed Young cue, which may be quite valuable. Some of the things on my list could hurt the value of the cue.
