Some TVS are unidirectional (one way), some are bi-directional (install either way). Get the data sheet for the part in question from mfg's website and see which it is.
Still don't know why you'd need the TVS or other protection circuitry. Doesn't the primary winding of a ign coil spike to a couple hundered volts when it fires?
I use a petronix ignitor in my 235, with a Bosch coil and ballast resistor. 12 volt conversion with the typical GM alternator and electric radiator fan and a small sunpro tach. Been running fine for about a year, including a 400 mile trip to Biloxi's Cruising the Coast last fall.
Your results may vary.....
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