Folks, the engine is all the way forward by the mast in a Tartan 30. I've often noodled on how I'd ever swap engines in my T30 if the need ever arised.
I can't imagine any kind of lever arm that long supported from outside the cabin that would do the trick. I believe I saw pictures some time ago of a rough gantry system someone slapped together out of 2X4s on the cabin floor to lift the engine and move it back to the companionway. From there I suppose you could use some sort of crane or external gantry to get the motor out the companionway and onto the dock. I've also seen folks rig the boom as a crane and move the engine that way.
One of my favorite T30 sites is the T30 makeover site at
www.t30makeover.com. Very inspirational what this guy's done with his T30. He has a couple pages describing the removal and installation of his A4 that might give you some ideas here
http://www.t30makeover.com/id51.html. Sounds like he just laid some wood on the cabin sole and he and some buddies muscled the engine back to the companionway.
Good luck! Keep us posted on how you end up doing this.