Originally Posted by BimmerKris
You can bolt the head and swap pistons with the early 318s it's it makes a huge difference. but that is all i know
I didn't know that...
Well that makes sense if its a pre-80 320i, where they were 2.0 liters. Swapping that head and pistons should effectively up displacement to 2L.
However the e21 he pictured is an 83 which has the 1.8L m10, like the early 318s, so I don't think you'd get that same gain. (correct me if I'm wrong)
edit: this is all from experience with e21s, I'm not as familar with e30s, though we share the m10.