Yeah... Olivia,
In my own experiences it isn't so much about how you look or your "appearance/presentation". Rather it has more to do with his expectations and his prejudices towards people who resemble our archetype.
It isn't your presentation that needs to be withheld from your father.
It is YOU that should be withheld from your father while he wrestles with his expectations, ideas and prejudices.
If you cater to him, if you try to spoon-feed him this *idea* that you are "trans?" then you will be conveying to him that this is a choice you have made, one that you can turn on or turn off with the flick of a switch.
If at all possible it would be far better to assist him in establishing in his mind that this is about YOU, not about a choice, not about a look you can put on or take off, not about a voice you can switch on or switch off. He needs to understand that this is about you having been born a female soul, with a female mind and this is not a matter of choice for you. Neither can you turn it on nor shut it off.
I would suggest giving him his space. What I suggest not doing is pretending that you can harmlessly switch it on or switch it off for him because like your father you matter. And someone needs to begin looking out for your health, safety and well-being. You have to begin nurturing yourself, you have (if you are anything like me) been starving all your life, having been denied the experience of simply being who you are.
So be who you are.
Your dad is a big kid now, an adult. Give him some space, just don't stuff yourself into a box for him like it is going to pacify him. You need to send a STRONG message that this is about you, it's not a costume or a game or pretend. If your father had just realized that you were actually another ethnicity would you paint yourself white and talk a certain way to pacify him? The degree to which you believe in yourself will be the degree to which your father believes in you, if he loves you in a healthy way.
Be strong.