Looks like a really interesting build. Any reasoning behind the hollow core in the column? It looks like one complex mold to build, you'd have to cast the entire column from top to bottom to maintain that hollow core, instead of laying it on it's back like what is more commonly seen. You maybe thinking of cost savings but it sure looks like a headache! Also, I'm not quite sure how well you could consolidate the EG from the the top down. I couldn't see it filling those webs near the mounting bolts. Also, what's the hollow core in the head for?
Also, what are you going to mount the rails to? You may want to consider adding some sort of machinable bar stock into the mold so that a true, flat and parallel surface can be machined afterwards. Don't count on the EG being 100% flat and true right out of the mold.
Just my 2 cents though..