I've seen E300D conversions with the valves mounted in various places around the engine bay. Some mount them under the intake manifold, some mount them to the sheet metal around the bay squeezed between stock components and some have brackets and mount them to the intake manifold. I am attempting to do this conversion with out removing the intake manifold, and I think 
the cleanest place is on the intake manifold. So I drilled and tapped a couple of holes in the manifold, and welded together a bracket to mount on the manifold. I also drilled and tapped the bracket so I could mount the valves with out needing nuts.For the Flat Plate Heat Exchanger
(FPHE) I welded together a bracket that screws to existing holes in the engine block right above the turbo. I know this portion of the engine compartment gets quite hot, but since the whole point of the FPHE is to heat the veggie oil I didn't see a problem with the heat. Here are some pictures of the FPHE and the valves.
