[Ironhawk]

Yeah you cant straight convert. Its too powerful in the early game and still weak in the late game. Having a fort add +10 to effective value of PD could be interesting.

Personally, I still think that the only thing you need to do to fix forts is to invert the costs. Make the fast forts expensive and the slow ones cheap. That way, if you really really want that fort up 2 turns earlier, or in a key mountain prov, you can do it. But otherwise, you will take the slow and steady route to build the fort that is "traditional" for your nation.