I'm not really following what you mean by "under the post". If you are referring to the stand under the wedge, just cut the angle iron to fit around it the best you can and fill weld around the cut. The box for the axle you can just use 2 pieces to get around that, just weld that in on the ends so it makes it a solid run underneath. You don't want any gaps as that would defeat the whole purpose of it. The center of the beam wants to go up from force so it will have to crush the lowest point or spread the highest.
Things that stick out end up being in your way and cause you to reach out more. That is one reason I don't care for splittlers with lift tables.