The chevy engines use 6 flywheel bolts and 3 locator pins. Looking at my old manuals, some of the GMC engines may only have 4 flywheel bolts. The 235/261 engines may share the same flywheel, but I'm not sure. 6 volt and 12 volt 235/261s used different ring gears. 6V models had 139 tooth gears, and 12 models had 168 tooth gears. The starter & starter pinions are also different, to mesh up with the different ring gears.
Good luck
chip
