Forget about mining LTC with GPUs. if you are looking for a profitable GPU coin look up Ethereum and Monero. A GTX 660 will not even be able to mine ETH but might be able to mine XMR, but it's probably not profitable.
It would not be profitable for sure when you intend to Mine XMR , if im going to choose i would mine ETH using AMD GPU because its more profitable for me hence i have a very cheap elevtricity here in my country. XMR is just a second choince though.
Both cards are rather useless when it comes to mining, profit wise it's a big question of would it even cover electricity costs.
Better just collect some funds to buy better GPU's, or forget about mining ideas alltogeather, it wont be worth it.