I'd pull the head that is on your motor and send it out to be checked before you buy a new one. It may have warped or cracked, but untill you pull it off, you'll never know. It may just be a blown headgasket. but if you see any cracks in the head, don't bother to send it to the machine shop, just get a new one.
Also, while it is off, you can inspect the block. If it's a blown HG, chances are one of the piston tops is really clean from pumping coolant out the exhaust - so you'll know where to check the HG.
If the cylinder walls are all scored up or if the deck is warped then you will at least need some machining, if not a new block.