At this point, there was nothing for it but to push some plastic through and see what happens - and so, in the spirit of "Hello, world!" (the first program you create when learning any new programming language), here's what happened:
(I'm just printing onto a piece of paper held onto the acrylic print bed with bulldog clips, 'coz I have no idea of whether the PLA filament would glue itself permanently to the acrylic and damage my nice shiny acrylic.)
OK, so it's not exactly "precision engineering", but I am SOOOOOO happy! It actually vaguely resembles the part I was trying to print. The most obvious
Anyway, a bit of research should suggest some possible approaches to get it to print more "solid" parts. Stay tuned ...