Most lights won't function correctly with a multi-spark ignition. The adjustable lights aren't accurate when trying to use to check total timing with the engine RPMs up.

Old non-adjustable Ferrets, old Sears/Craftsman/Penske inductive lights (2134, 2138), and any of those sold by MSD will. Adjustable lights should be avoided. Plenty of the old Sears lights on ebay, and occasionally, an older MSD chrome light or even a Ferret 81 show up. Or you can pop for a new MSD copy of the Ferret, MSD also does a battery powered unit. I think they are still made in the USA