I prefer this deck without purify, focusing more on SoPa. With SoPa, you don't need to use liquid shadow until you get rid of the shard, and by then you won't need purify. That being said, I would cut down to 30 cards to make drawing SoPa more likely. I'd say -4 purify, -3 water pillars, -1 steal, -1 siphon, -1 dark tower, +1 SoPa and swap pendulums for dark towers.
If you want to go the purify route, I'd get rid of SoPa. It seems like it would only slow you down if you don't need it. You definitely don't need so much water quanta. It will take a couple turns to get dragons + LS out anyway. Off mark alone you'd be able to have 2 vampire dragons with purify by turn 4, which is about how long it would take to get enough dark quanta to play 2 dragons + 2 LS anyway.
And I personally don't like having only 1 of a card in a deck, so I would go either 2 dusk shields, or 2 vamp daggers.