If there is another ring gear that would fit, it might be from the 9.5-inch truck axle. It's a semi-floating 14-bolt (I think it was semi-floating...). However - ZL1's ring gear is 9.9-inches (9.8XX").
How about a taller DR? Redline ran a slightly taller Mickey Thompson DR on their car if I remember correctly. That might be worth looking into. It's in the current
GMHTP. I think it was a 305/40/18 or something. It would require you to go with a smaller wheel, but it sounded like the tire was taller, which might be a solution.
If you rev' higher, it'd probably be a good idea swapping valve springs/retainers for valve float. ZR1 features forged slugs, titanium rods, intake valves, hollow exhaust valves and better valvetrain, and it's limited to 6600. I'm not saying you couldn't take LSA to 7000, but it was my understanding blown motors don't like being over-rev'd...
JMVHO. I wish you luck
