Identifying E30 engine from donor

[daklunk]

Could someone tell me how to identify an E30 power plant by looking at some external part of the engine? I have an 84 318i that had the engine swapped from an 85 320i... but it's not a 6 cylinder, it's a 4. All the web sites I've looked at show that E30 320i's came only with 6 cylinders (M20). Is there some way to tell which engine I now have in the 318i? It will have moderate performance upgrades, knowing which engine it is might come in handy.

Thanks