I would leave off the counterbalance arm for now. In the case where they redesign the arm, it's possible that they'll refund some $$ for your arm if you haven't used it yet (drilled through it). The SB may just be an "inspect for..." bulletin.. so obviously it's impossible to say for sure if delaying will benefit you..
Short is, if you have other things to keep you busy, go do it and come back to this later. You won't need to have the arm mounted until you permanently attach the stab to the tailcone.
Rob Carsey, Winfield Park, NJ
RV-12iS (N713) / Completed 12/2020
ASEL, Glider, AGI/IGI, LSRM-I, FCC GROL
or ADSBExchange Track