They are completely different buggies. They don't swap parts at all that I am aware of, except the big bore shocks that people put on their H8's.
You can get the H8 a lot cheaper than that off of ebay. I have seen them new in box for 389.00 plus 15 bucks to ship, if I remember right.
They come pretty much built (the H8), but you'll want to take the diffs out and put fluid in them, so that will give you a chance to disassemble it.
I'm not aware of any other way to buy the H8....