Hi Andy!
Best of luck on your Nomad restoration project; please keep us advised as it progresses. Photos are always good!
I've used QuickSteel and was very pleased with the results. Of course, its suitability varies with the application, but I found it worked surprisingly well at filling grooves in drum brake backing plates and any number of less common uses. It is heat-tolerant up to 260°C/500°F, so you should be fine with the powdercoating temps. If all you need is a cosmetic fill of the dent, it should work well, as it remains pretty stable dimensionally after curing. I found about 1% shrinkage with normal curing, up to 3% with heat-curing, so I'd suggest applying it and allowing it to cure at room temps.
If not a re-do with black, do you have an idea which way you might be leaning for color? That bronze and black would make a nice, durable finish if you decide to give your re-do a redux.
All the best,
Dan.