fresh 4l60e leaking from inside bell??????
No matter what the cause of the leak, from here we can only speculate. Either ways you're going to have to unfortunately pull that thing and check it out. Doing that will give you your answer pretty quickly.
I also use two bolts/dowels to align the pump as it goes in; these can be seen in the picture.
Did you remember the paper gasket between the case and pump?





