Love the idea! Since its discarded right away when it captures, there isn't really a need to convert fortress types. I'd word it like this:
"Contents gain 1/1 each turn. If occupied and a Roman enters play, capture contents to your opponent's Land of Bondage and Capture a Human Hero to Discard this card."
It's ever-so-slightly different, but it didn't make sense that the contents of the Garden would be Discarded in order to capture someone else. My further suggestions would be to make it a Sadducee instead of a Roman (the Temple Guard arrested him, not Roman soldiers), remove the Discard portion, require the contents to be increased (so you can't use it the turn you put it down usually) and make it only hold N.T. Human Heroes. It'd be a great soul-gen option for the offenses that can't use Melchizedek while being balanced by the need to keep feeding your own Heroes to your opponent's LoB in order to get the soul gen (although you could use other cards to get the capture portion free without gaining the soul gen).
