The inductive pickup will definitely work. Spark plug wire voltage is essentially the same on 6V and 12V systems, around 20,000V.
The issue is the display, which Innova says needs between 10 and 12V. The solution is to use a separate 12V battery to power the light.
From Innova's site:
Does my timing light work on 6V systems?
Your timing light may be used on vehicles with 6-volt electrical systems by using the following connection procedure: 12-volt automotive battery required.
1. Connect the RED battery clip to the positive (+) terminal of a 12-volt battery.
2. Connect the BLACK battery clip to the negative (-) terminal of a 12-volt battery.
3. Using a length of 18AWG jumper wire, ground the negative (-) terminal of the 12-volt battery to a known-good ground on the vehicle under test.
