Make sure that the starter drive gear is fully engaged to the flywheel teeth depth wise, but NOT pressing "hard" against the flywheel at ANY point in the full flywheel rotation. Also, it needs to be properly aligned with the plane of the flywheel, so that the teeth fully engage. This may require washers for the mounting bolts, etc.....
Maybe you can see this thru a bottom access port in the bellhousing, as someone else rotates the motor by HAND, and maybe turns the starter motor over slowly, with the COIL wire pulled?
Be sure to fully support that car with jackstands, not just on a jack!!
Just to be safer, I also usually lay a spare wheel/tire from my old 4 x 4 , on it's side, under the car, below the car frame, near me, just in case, it will stop the fall before you are crushed!
Just an afterthought !
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James Madison, father of the Constitution, said, "If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy." He also said, "No nation could preserve its freedom in the midst of continual warfare..."
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