There are different angles of the bolts into the heads with the later fuel injected engines---and the later heads are more readily available in some areas - so be careful of what manifold/head combo you buy-----

Being a Ford guy every since being a mule team driver----I was always harped at about the chevys all being the same while the fords were all mixed up on parts, but let me tell you one simple fact----try being in the race engine machining business and you will see very quickly how many different versions of the chevy engines there are-and its not always drivers or passengers side dipstick----------------