Ditto to what RJ said, assuming your lathe isn't modded with a variable speed drive means you're attempting to cut a thread at 150rpm (your lowest speed). Pretty hairy at the best of times. I suggest you use the method put forward in the video, its your safest option and considering you are cutting ally at a fine pitch, your depth of cut will also be small, potentially minimizing the chance of chuck rotation.
I have variable speed drive on my G0602 (ideally its now a G0752) and I'm able to dial my speed down to about 20rpm but I prefer around 40-60rpm because I get a better finish when screwcutting. I also have a built in brake which stops the chuck within a second and I've never noticed a movement in chuck orientation.
I made a spider once to fit the lathe, and I actually removed the chuck and work together from the spindle to check the thread on the other end of the spindle for fit a number of times. Upon reassembly no change in crosslide position was made to check for motion on first pass. I never had an issue that day.
I think your only issue should be work stickout. If short its ok, but if long you need to support the end and work around that.
As Mach89 mentions, an upside down tool is handy. I have a boring bar permanently set upside down in its toolholder for when boring deep holes, I run the spindle in normal direction and bore the opposite side of the bore. This way I can see what I'm doing without hanging over the lathe and upsetting something.
If machining brasses and bronzes I make a chip deflector out of some brass shim and fit it to the tool clamping bolt closest to the working end and form it to sit above where the action is.
This saves me spraying the surrounding area and myself with swarf.