How to tell the difference between a 3.4, 3.6 & 3.8?

[itsnotanova]

I'm about to go look at a stash of Porsche parts a guy has. He supposedly got them from a friend and doesn't know much about them. He has two 3.6 engines. I can quickly tell the difference between a 2.5, 2.7, 3.2 and 3.4 from the outside but I've never seen a 3.6 or 3.8 up close. Is there a quick way to tell if the motor is a 3.4, 3.6 or 3.8 without looking at the serial number on the bottom?