Well, since nobody else has chimed in, I'll give my two cents worth...
From the sounds of it, you can probably very successfully pull off the tall, androgynous male model look...your handsome features work both ways! How many male models have we seen that are gorgeous as guys, and with a little bit of makeup look just as gorgeous as women? (I'm thinking of course of people like Andrej (now Andreja) Pejic here).
It sounds to me that you are in a good position to "soften" up the edges and easily achieve this look. Your height at 6 foot, especially if you are only 178 and carrying some muscle, is not a bad starting point. If you just lift lighter and increase your cardio, you can probably get leaner with less muscle and drop 10-30 lbs, depending on how you look and feel. A healthy weight (on average, based on BMI) for a male at 72" is somewhere between about 145-185 lbs. Your goal shouldn't be skin and bones, but you can very likely look more soft and less muscular with a little effort. As for diet, I am a fan of everything in moderation and controlling your overall daily calorie intake, instead of trying to micromanage everything you eat...but obviously try to minimize (not necessarily eliminate) the processed foods, sugars, flour and saturated fats. If you are healthy now, then you already know what to do.
You can grow your hair out a bit...maybe a shoulder-length cut that would work both ways. If you are comfortable, you can even start on the little things, like cleaning up your eyebrows, maybe pierce your ears (if you haven't already). You should be able to present as a tall, dark and handsome guy when you need to, and with a more feminine styling of your hair, a little makeup and clothes, you should be able to present just as convincingly as a tall, dark and gorgeous woman.
If this works for you, I can't think of a better position to be in...you can (hopefully) pass both ways and find what you are most comfortable with!
Good luck!