Are the M96 heads interchangeable?
 

Quick question. Are cylinder 1-3 and 4-6 heads interchangeable? I know the scavenger pump needs to be reversed but are the cams and the head itself the same?

I have a almost complete 2003 motor in my garage on a engine stand. The heads are different. 123 head chain tensioner is on the bottom the 456 head its on the top. The AOS connection on 123 is different than the 456 head crank exhaust port. I have a complete set of 2004 heads off a 3.2 they look almost the same and also could not be switched for the same reasons.

That's interesting, I've never seen them but always assumed the heads were the same, so that they could save money using just one casting for both heads. Are the differences something that was machined differently on the same casting? Otherwise I'm struggling to understand why they would design an engine with one timing chain on the front of the engine and the other at the back.

Ok, I see what you are talking about, but it looks like the AOS on 123 is the same hole used for the cam tensioner on 456 and the cam tensioner on 123 is just capped off on 456. I believe it is the same casting but with different "accessories" and/or machining.

There seem to be a lot of cracked 123 and a surplus of 456 because of this. Which got me thinking.... which led to the question.