Ok. simply because everyone needs to learn this eventually, i'm going to hold a small, short class.
Part 1
Engines come in different flavors cylinder-wise.
1, 2, 3, 4, 5, 6, 8, 10, 12 etc.
I've never seen or heard of an L7 [Inline=L] but if anyone does know of and can show, please speak up. Anyways, moving on.
We'll just concentrate on our cars.
I've only seen 4cyl's come in 2 variations: Inline, and Boxer. Inline is denoted by 'L' before the # of cylinders. Hence MY Avenger has an L4 engine with the engine code '420A DOHC'. A boxer engine has an 'H' configuration. But talk to the porsche boys about those.
6 Cylinder engines I've seen in 2 configurations also: 'V' and Inline. You already know what Inline is if you've been paying attention... JBI, please stop throwing paper balls at Nykon. He'll throw an engine block back at you if you're not careful. Now, 'V6's are called such because the cylinders create a 'V' shape that splits the cylinders into 2 seperate equal numbered halves; one on each side of the block.
Part 2
Each cylinder requires an exhaust port as well as an intake port. These 2 different ports are located at the top of the cylinder via an Exhaust Valve and an Intake Valve. there are very few engines [if any that i know of] that require 2 intake manifolds, so there will always be 1 intake manifold. On an engine with the 'V' shape configuration [basically any engine higher than a 5 cylinder] there will be an intake manifold sitting on top of the engine, between the two sets of cylinders. This manifold will service both sides of the engine.
The Exhaust Manifold however, has to be placed on the OUTSIDE of the block. Since there is no way to use 1 manifold for all the exhaust ports, 2 manifolds are used. With these 2 exhaust manifolds, there will be a left and right side or front and back, depending on the vehicle. But there will always be 2 exhaust manifolds.
Figure: 4 cylinder engine

Figure: 6 cylinder engine [NOT the one in the avenger, but for this it will do]

The reason why the V6 won't fit is because it has 3 exhaust ports per exhaust manifold. Why did I not say that to begin with? Simple: Simply saying it won't fit is one thing. But if I can teach you truly WHY it won't fit, then, I have accomplished something by teaching you something you need to know [if you didn't already that is]. And if not you, then someone else that hasn't been taught.
And for a little bonus if you paid attention to all of this

Hope this was educational for you.
-Shiano