I get carried away here, but I hope this helps:
You need the full 3D file of the casing, not just 2D drawing of elevations/sections.
Something like .dxf or .dwg or other graphics file with all the proper surfaces finely mapped. Its this file which the CNC machinist/machine will use to cut the casing from.
However, I don't think just changing to billet steel will solve the problem.
Sadly, and I don't mean to sound negative, but I will be amazed if Nissan give the file out, simply from a copyright and intellectual rights bollocks viewpoint.
Try it, but I think you're looking at needing to give the casing to someone who has the ability to map it digitally as already suggested. Without some stress analysis work on this model, you could just add say 5mm to the wall thickness of the casing where possible (avoiding fouling with rest of car), but this is guesswork and someone has to edit Nissan's original model of the casing with the extra 5mm before it can be machined (possibly quite specialised work).
You might be better off mocking up one of the casing with all the plates welded on that you want. If this casing is then scanned, the machined casing will have the extra thickness built up in one material.
Out of interest: I know people have come up with very good ideas for welding on plates and/or bolting accross brackets. Ultimately though these only provide marginal additional strength, mostly because the extra through thickness of the casing does not work compositely.
A bracket with the same thickness as the casing does not double the stiffness of the casing wall. One plate 20mm thick is 8 times as stiff as two plates 10mm thick working seperately.
If you ever get this file, perhaps I could have a copy. A few weeks of FE analysis and I should be able to help show where its becoming overstressed and how much thicker it should be. It is perfectly possible to build a new model file with the new thicker design, as ultimately that's what the CNC shop will need.
Jim, you can come up with the forces...
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