I've made some progress, getting the tiny renders and line art to scale:
And now I have a front, back and sides view to full size and the helmet renders also to full scale. My file shows the helmet as being just slightly over 10" long in the renders. Looks comparable with the MA/SA helm.
So next step is to print off portions of the line art and see how they match on me. I scaled Bo to being 170cm high in footgear which is close to me. She winds up as 174cm using the troopers as exactly 181cm high (6').