Wow, a 28gram brass headshell weight and 100gram counterweight add on?! Someone correct me if I am wrong but I think that is an extreme concept and probably not the best one. Instead maybe you could add a couple of stainless steel washers under your headshell screws atop the tonearm end where the cart mounts. If I had to guess I'd say you would be much better off going this direction over adding 128g of solid brass to your arm!
I could be wrong though so maybe someone with more knowledge can share their thoughts also.
I could be wrong though so maybe someone with more knowledge can share their thoughts also.