Users, take note, I've updated the website with a more simple un-cheatable method of getting the winner! I decided to also use USA Mega Millions numbers as one of the random inputs. See bitlotto.com for details.
You should still use two blocks, otherwise there's no reason to use block data at all. Otherwise, this seems quite sound.
The only reason I use a block is I figured feeding more random data into the hash helps it be more random at the end.
I also wasn't sure if you calculated all the combinations of Mega Millions and tallied the first digit of the hashes perhaps one of the 16 letters appears a couple times more than the others as the first digit. Feeding a block hash into it, eliminates any letter from being more common as you are adding a block hash... I never did do the calculations but it does make the final hash better IMHO.