User blog comment:ACWeapons/RWBY Genderbend Conversion Chart/@comment-25110963-20151225073828/@comment-26397825-20151225091553

Eyes can be made slightly sharper or softer, so keep the base shape but give it a slightly different feel dependant on whether they are male or female.

Muscles and chest sizes...muscles are a bit easier as you can kind of base it off their fighting styles. Blake would probably have stronger shoulder muscles, but overall would be wiry. Weiss and Ruby would be thinner because their fighting styles don't call for larger muscles. Yang would be muscular in the arms because her fighting style revolves around that.

Chest sizes...well. No matter what you do, someone is going to say 'That's wrong!' I would say just go with what you think suits their fighting style and personality; big boobs can get in the way of fighting, but Yang flaunts hers because it suits her personality. So someone like Sun would possibly have medium sized breasts that she binds, to keep them from getting in the way. Mercury may not really care either way, but might have smaller breasts naturally.

It's a subjective thing that is dependant on the artist themselves. Just...don't go giving every girl a big chest and it should be fine.