I have great sympathy for the struggle some people endure to find and express their true nature, and to become comfortable with themselves. In this case, a traditional fraternity is not a good solution - not for the trans person, and not for the fraternity.

First, falsely presenting yourself at Rush as a male (when you are neither genetically nor phenotypically male - when you have only been taking testosterone for a few months, when you are using a compression wrap to flatten your natural female breasts, and when you don't have a dick [you both have post histories]) - well that's a purposeful and important deception of the men you are seeking to bond with. We don't tolerate deception. We don't tolerate liars or their lies. And the deception would certainly be discovered. You clearly have no idea what the culture of a fraternity House is like. Many older fraternity Houses have gym-style gang showers, and guys shower together in the mornings or evenings just as they always have at the gym or after practice. It's common for guys to hang out in their rooms in just their underwear or sweat pants.

You cannot spark a bond of Brotherhood with men you are actively deceiving.

So your only option is to Rush as a pre-op trans person, as an intact woman who wants to be a man. And most traditional fraternities are unlikely to surrender their male refuge to a live-in girl pretending to be a guy.