The final trick was to change the horizontal line pattern line spacings and weights to a multiples of 1/600th of an inch (the printer resolution) and then to pre-rasterize them to 600 dpi monochrome bitmaps with anti-aliasing turned off. These could be reliably previewed at high magnification and placed in InDesign without scale changes. The printer then produced nice clean lines without transparency artifacts.
Next to finish the resume--which I expect to have done Friday--and then to start pounding the pavement. Anyone want to hire an architectural intern?