Welcome back:
There should have been a mark on the timing gear. I don't have anything saying location of the shear key. It could have been at 12 oclock, but usually there is a round mark on the pulley. The mark on the timing gear should have been at 12 oclock. If you replaced the gear, look at the old one and see if the two align.
As far as determining TDC now, there should be a mark on the crank pulley and indicator on the front of the engine. On the indicator, you will see degrees of advance and there should be a T or a TDC indicating top dead center. You will need to align the T with the mark on the flywheel. See pic 2
Let me know if this helps.
Joe
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Saturday, October 19th, 2019 AT 5:28 PM