The following installation photos provide some visuals, ideas on where and how to install these fire extinguisher systems in both, 911's and 914's race cars.

I like this particular orientation of the Heinzmann bottle https://pbase.com/9146gt/image/162585821 for areas where height-space is at a premium, like just under the 100L fuel tank at the front trunk of a 914-6 GT. Laying down the bottle on its side makes perfect sense to me.