In the past I have carefully drilled and tapped a drain hole in the TC, for an Eighth pipe plug. But I gotta tell ya, it is Nerve Wracking, and the guts are right there.
In your case, accepting what you said as gospel, I would just fill it up and drive. Done it many a time.
As to the fluid, read the label. AFAIK all Dextrons can be mixed; but I do prefer Dextron II. I did one time, a long time ago, fill my Mopar with Ford juice, but that was a bust; It was just too slippery and I had to take it all out.
