Estimating the fat content of homemade chicken foot gelatin
From experience with gelatinous stock from pig bits, I've found that gelatine can seem fatty, when really it's not - and gelatine is good for you in ways that fat is not.

I think your tall, narrow container idea is a good one, but first get it up to liquid temperature, and then keep it at that temperature for as long as it takes. You'll want to avoid convention currents, so take it off any direct heat. It might be enough to wrap it in a towel, or maybe you'll need to leave it in an airing cupboard or even a low oven.

Given long enough, even the emulsified component should separate out - although I can't guess whether that would be hours, days or weeks!

This does mean leaving the stock at a bacteriologically unsafe temperature for a long period - so the stock you test in this way should not be eaten. Do it on a small sample.