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2 & 4) If you can get the stamped pulley off without distorting it, it could be used. Maybe try tapping it in a little bit so you can clean the shaft for easier removal. KROIL is a better penetrant than PB Blaster but a homemade mix of 50/50 acetone & ATF works just as good.
A cast iron pulley is a much better choice.
3) Yes, uses a key
Jeff