Damaged trans?

Yes I have never seen a 904 explode a drum either, probably just because of the smaller mass. However it's still possible for it to do it, I wouldn't be over confident that it wouldn't explode and never say never.

The 727 outer race is pressed into the case and they tend to break the case when they roll. Thus the need for a bolt in sprag. The 904 already has a bolt in or riveted in rear sprag already so buying one isn't necessary unless yours is damaged.

A basic stock rebuild is fine for your application, mine is pretty much stock with a 5 disc front clutch, and an A500 front pump with the flat drive pump hub on the converter. That's the only thing I've really broken in my 904 is the converter drive hub.