Back in the day ATF was used as fork oil. It's probably fine, but... :hehehe
How much is a QT of real deal fork oil? :dunno2:
I would use more modern fluids designed for suspension work. The biggest problem I have seen with modern ATF is that the viscosity is all over the map, from 5-10wt. And it's not really advertised with a viscosity. (now I'm sure you can find it on the MSDS, or BITOG's forum), but why, when you can get real suspension fluid, probably around the same price as a good ATF, and you will know the viscosity. I think this is important, if you are trying to fine tune your forks and want to try different viscosity's to change the forks character.
If it were me, I wouldn't hesitate to use ATF, in an emergency situation. But for all others I would just get a QT of fork oil, IIRC a QT will do around 3 fork legs...