chevy 250 rear main seal replacment / oil pan gasket
 

I am replacing the rear main seal on a 1966 c10 with the 250 motor. with the motor in the truck, I now have the oil pan unbolted , need info on how to remove the top half of the ... rear seal ... with it in the truck and crank in place ??? also looks like I must jack up the motor to get the oil pan off to clean it up and replace the gasket ? so , how to remove the top half of the rear seal and how to slide the new one in, and do I jack up the motor to get the oil pan off ? please help !!