How many tractors with bypass filters do you suppose Ford made? Millions? They all came with hard lines. Since the filters are attached rigidly to the engine, there is no movement to cause metal fatigue. Same deal with manifold mounted filters on Chevrolets.
My belief is that, since Chevrolet trucks didn't come with the filter, it was up to the filter manufacturers (Fram etc) to come up with a way to plumb the lines for a number of different configurations of engines. Soft lines would have been the most forgiving for minor variations between engines encountered. Steel lines would have been more economical, so it wasn't about saving a few pennies. Just my 2 cents.
Carl
