I have a tool at the shop that "listens" for fuel injectors clicking and lights a light whenever it detects the noise. It might be adaptable to trigger a timing light. I wonder if it has a manufacturer's name on it?

While the procedure to check timing with the drip tube is more involved, once the timing is ensured to be correct the light is a great way to monitor for change over time.

Oldest specialty tool I've used? Hmmm... Does using the original jack from my '36 Plymouth count? I've got some tappet wrenches from the '30s as well. But I think a starter growler made in the '40s is probably the oldest specialty / diagnostic tool.