I did it without buying a harness in my 95 9C1.
I didn't want to lose the stock cluster, so I added the Z-cluster wiring in to the existing wiring, so I could use either cluster. I obtained all of the wiring pin-outs for all three connectors (Caprice/impala cluster uses two, Camaro uses one) and did it.
There are some modifications you need to do the the Camaro cluster before you can install it... adding jumper wires, cutting traces, etc.
You will lose the transmission position indicatior (PRND321), You will need to convert your oil pressure sensor (some/none) to a sender (9C1 is 0-80 psi, there is one for a pickup that is 0-60 psi) and modify that wiring, and add a tachometer output wire to your PCM wiring harness.
The low fuel light circutry for the B-body cluster is in the cluster, but in the F-body, it's not. I used the low fluid warning center out of a 91-93 caprice/roadmaster and made it work for my car.
PS... Two weeks after I did this mod, I realized that I missed having a digital speed readout... so I installed an HUD from a similar vintage Pontiac Bonnevile SSEI