Well. I just managed it. I broke... a diamond pickaxe. Mining obsidian alone. That's right. I now have 1562 blocks of obsidian... on the nose. Enough to make a 15x15 tower - shell only - 26 blocks high, with some change.
Which means, I'm about halfway to the goal. I cannot tell you just how exhausted I am right now, after having made that damn Nether run so many countless times... However, I'm quite proud of my resilience and patience, just mining that one block over and over and over and over and over...
Sigh... Regardless. I'm not gonna be awake and around by the time 1 PM rolls around, which is when my 48 hours are up. So, I'm gonna skip right to the good part and http://www.mediafire.com/?l75d92aiz6pm4gr to do with what you will. May the fruits of your labors turn out more than just a chest half-full of obsidian like mine did.
Oh, and Mr. E... That minecart tunnel of yours. You burrowed right through two coal patches that were annoying me greatly every time I passed by them in my little cart. So after I broke my diamond pick, I stopped by in that tunnel with the stone one and chopped out all the coal. Came away with about 20 coal, after which I replaced everything I mined with smooth stone. So now your tunnel looks a little bit more pristine.