I modified the starter weight on a set of old enfo weights and put on my MX. But I didnt do it for loader stability. I did it for more traction pulling logs, and pulling the transport disc and 3-14 plow with loader off.
I dont know what your terrain is like, but it would seem like nothing is needed. half a face cord is ~1/6 of a cord.
Average cord weighs 3500#.....so you are only looking at ~600#.
If I understand correct you dont have anything on the back because you dont want to bang around a tiller or box blade right?
My two suggestions would be 1. fill a barrel of concrete and attach to the 3PH for your counterweight.
or 2. Buy, or build a carryall and carry wood on the back of the tractor. Load it first, then load the loader