Hmm... my english is as rusty as my thoughts are cloudy!
I'll try to explain (but thus is really just a brain-storming activity, no need to take it seriously). Remove the name "Castle" as such structures were virtually non-existant. Rename it "Military" and we have 8 new slots to fill with different kinds of military investments which can affect retinue cap, troop quality, local levy reinforce speed etc. first hand, defensiveness and fort level second. Remove the namne "Manufatories" as such economic activity were virtually non-existant during Gempei. Rename it "Specialization" and you have 4 slots and 8 choices for representing investments in regional economic activities to expand tax revenue, supply level etc. first hand, retinue cap, hiring ninjas etc. second. Having only 4 slots and a steep prize, it goes a little way in representing path dependancy, where as starting to develop a region in a certain direction usually becomes its defning feature. Or something like that.