I quit using timing lights years ago.
mostly due to the rubber on the harmonic balancer slipping.
My dad taught me how to use a vacuum gauge to set timing. Hook it up to manifold vacuum and set the carb idle mixture to around 18 inches,turn down the idle to 500rpm or so,turn the dist until you get the highest reading and back off 1or2 inches of vacuum.
This has worked on everything from a '47 ford 8n to my CJ7.
