I wish to port a Wordpress theme - with all of it's benefits (e.g. auto fitting based on browser window size, iOS version, etc.) - to Tumblr.

Why? Because I believe this theme surpasses every other I've come across. And since IMO Tumblr is preferable to Wordpress (I am not wise enough for Wordpress).

not a chance, unless of course years old get it done manually :). Sorry!