The flares we used are the Skidz Flares. They are a cut out flare and require cutting the fenders. They do look similar to the ZR2 flares, but are vastly different.
To the best of my knowledge no one has fitted ZR2 flares to the stock crewcab body work. Even the front fenders would require modification as the ZR2 fenders are larger at the wheel well openings to allow for the mounting lip inside. I am not saying it can not be done. I am sure it could, but it would take lots of skilled work to complete.
You can download the GM Upfitters manuals and compare the frame and bodies. It would take lots of work to add ZR2 flares. Maybe much more than most would consider. I still think the best option is the stretch and add a standard size bed. That eliminates the hassle with the fuel tank and mounts.
If you must have flares , the last set of Skidz falres are for sale in the classifieds. That is the easiest option. Just the Skidz cuts looks very good if you can go flareless.
I am still waiting for someone to try the F150 flares. They looked great on a Jeep I saw a picture of. I still think those have potential
I don't know if Mike Copeland still sells his pocket flares. Those might be another avenue. It would need the standard S-series bed sides though.
One more thing to consider would be the baja designs fiberglass fenders. BIG bulge fenders. Cut and fit