Cast iron? Do you have a foundry?
I think the keys to moving them would be a good game plan, some extra hands and perhaps some short, padded bucks to lay them on their back edges and not put a lot of shear force on the base. They're not fragile, but like any piece of furniture, they're not what I'd call bomb-proof.
MDF, in spite of folks not loving it, has some distinct advantages when it comes to speaker building. Without getting into hyper-expensive exotic sheet material and associated machining cost, MDF has far more positive attributes than negative. Also, the MDF that Jay and Don use for cabinets is not garden variety stuff. It's the best the industry has to offer.
