If you need any start or launch retard ability the MSD digital 6 is an option, it's also potted so its pretty water resistant unlike the 6 al ( ask me how I know ) Ha ha ha...
We have used one for several seasons now with no problems.
If all you need is a box with a limiter the 6 M2 L is probably easier to get a BBC head mount for.
You can also check out Daytona Sensors.
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