When ordereing a harmonic balancer from www.gmpartsdirect.com
it is ok to use the part number they have listed for your car. The updated balancer will be sent to you, and the difference in price will be accounted for in the end.
I had a chat with someone at GMPD about it. I initially ordered the original part number, called and cancelled it, then ordered the updated balancer online. I then got an email invoice confirming the cancellation, but with the new part number on it. I called to make sure I would get the corect part and no one had messed up the numbers. The person I talked to told me either way, I would have got the correct balancer and charged the correct amount. This may apply to any updated part.
Their phone number is 336-760-7046
Side note, when calling that number, you may get a parts department, performance department, or a Flow Chevrolet switchboard operator, that when asked for GMPD, will direct your call to an automated line that you can leave a voicemail on. If that happens, call again, you'll get someone to talk to eventually.