The throttle body has a gasket, because the coolant actually flows through the throttle body. The gasket is cheap and easy to replace.make sure your LIM gaskets aren't leaking as well.

You can do a Gen V top swap, but you need an L67 drive by cable throttle body, which in my opinion is better since there's no lag.

As for a DBW throttle body, you may be able to, I know Bill did the opposite to an L26, but I think it's pretty complicated. I'd stick with drive by cable is I were you.