Which rear main seal

I am dealing with a remanufactured engine in an '87 TC w/auto trans. I need to have the oil pan gasket and rear main seal replaced. I have located an oil pan gasket, but the parts guy at Ford says he needs the build date before he knows which rear main seal I need. Since this is a reman. engine it is very probable that it will not be of the same build date as the car that it is in. He says that the older part # is a 2 peice seal and the newer # (E5ZZ-6701-A)is a one peice seal. Any suggestion on which one I should get?

I can't find any notes on what year they made the change. You could order both and return the one you don't need. Or wait until you pull it apart and then order.

Is the 2 piece seal replacable with the 1 piece? Or are the engines actually different models that take different seals?