tungsten you say that sounds alot easier then what I did, I welded more metal on the counter balance and then machined it, also ground down the rod to a airfoil shape and ground out some of the piston. I was able to remove about 1 gram, still barely got it to balance [OS .32 FH] did some work on the ports too, chamfered the outside bottom of the ports to get better flow. Haven't had a chance to run it yet. On automotive racing engines the counter balances are airfoil shaped to reduce drag.
Thane