I was involved with one of the Gibb automatic ZL-1s some years ago.
Back in the day a ZL-1 with headers and a good tune up did around 525 hp. With todays piston rings and oils they are around 550 hp. That's on race gas and under dyno conditions. Check out the COPO report on this site for more info.
The AMA specs don't directly specify a stall speed but state the "max ratio at stall" is 2.1. They will idle in drive just fine but there a few caveats. Most if not all automatic ZL-1 Camaros were built with the #4346 780 cfm vac secondary carb. The AMA specs call for the #4296 850 cfm carb. Original ducted hood air cleaners had a vent tube with a 90º bend. This tube will contact the rear pump lever on the 850 generating a constant fuel stream; this may be why they were built with 780s. Later air cleaners had a revised vent tube that will clear the lever. ZL-1s do not have manifold heat; there was no choke and they cannot have a heat-riser. So do not build your ZL-1 with a heat riser and the wrong air cleaner. I do not have 1st hand experience but I hear the 850 is too much for any kind of street use.
Somewhat related, later CX TH400 Camaros used a fast-idle solenoid. I do not know if any ZL-1s had it; the engine bay photos of #5 ZL-1 show no solenoid.
The ZL-1 I learned on has been in storage for nearly 15 years. Ask Santa to give me a call!