By the looks of that gen5 ZL1 diff, they changed the rear diff cover to match the gen6 subframe bolt in spot.
Looks like we would also need the axel stub-in to get our axels to work with the gen5 diff.
For anyone unfamiliar with the gen5 diffs, here is agen5 SS on the left compared to a gen5 ZL1.
I have a gen5 SS 3.27 diff sitting in my garage I would love to stab into my car. It seems in the realm of reality to make the swap possible, and for a decent price. A custom rear diff cover should run about 150-ish without a built-in cooler, and about 230ish with one. I'm not sure what the axle stubs would cost. 50ea? So about 350-400 to swap in a 5gen SS diff that comes with 3.27 - 3.45 - 3.91 in them factory? Or if you don't like those ratios, there are plenty of gear sets available
I'm sure a kit to use the ZL1 would be closer to 500, but that diff is huge and bulletproof. They come in 3.23 and 3.73, an as far as I know, have NO gear sets for that 9.9 rear end.