Well another failed attempt and a burnt finger later, and I just wish we could get hold of D-90 or 180 over here in the UK!
Robert - the blog (part 3) addresses the acid (for inversion) thing, saying that very little of the mix needs to be inverted before progressing, in their view. However, I didn't have dextrose to hand this time, so I guesstimated a tbsp of golden syrup, which is partially inverted, and prevented crystals well into the attempted Maillard phase. I say 'attempted', because my lime clearly wasn't enough or as effective as in the video on that blog. I had crystals gathering all around before I got the darker colour and had to stop before getting there.
I'm not sure how many more attempts I can face - it's a lengthy process of trial and error!