Well you will need some aluminum tubes and sheets, I have a quick SolidWorks 3D rendering of one, its by no means to scale I just threw it together. The red lines in the first pic are where
the welds would be for the tube and sheets.
Here is an example of a FFIM using the stock lower intake manifold on someones car.
__________________
Whats in the garage, well.... in the yard.
1986.5 Toyota Supra - NA - 5 spd
1986 Ford Ranger Lowrider - 5 spd
1984 Ford Ranger XLT - 7" Lift - 4X4 - Auto
"Stuck in the 80's"