I saw it in person. There is about the same amount of room under the hood as the 99-04 Mustangs. The plugs are on the manifold sides of the heads, just like the 99-04 heads. The difficulty in changing the plugs will be about the same.
The exhaust manifolds look relatively easy to get to, but they look like they flow great, so shorties will be a waste of money, only long tubes would buy you anything.