Could be the rear seal too. That's a really easy one too. Just pull the driveline and pry it out, then tap in a new one with some sealer on the outter edge.

 

Here's my 2 cents worth, if you haven't already finished this project, you might want to look into a one piece oil pan gasket, it isn't going to be easy to do upside down but, you'll have to clean the pan rail and the oil pan itself, do this really well cause if you don't you'll have more leaks. Anyway the one piece pan gasket is rubber and has steel inserts around the pan holes, so you can't overtighten the gasket and tear it. We had an oil leak on our Big Block and ended up pulling the motor to fix it. It don't leak now. Good luck.