SLI w/ GTX 660 3gb and 2gb

I don't think many of you have seen a gtx 660 has 3gb but there is one. it came with the prebuilt pc that i got a few years back and it is from Asus. I was wondering if I would be able to SLI this with a 2gb card, I was hoping to buy a GTX 660 Twin Frozr. Can someone please answer me asap before I make my purchase? I understand that the effective memory may only be 2gb, which i am fine with.

You can do that, and you are correct the effective memory total would be 2GB.

is it better to make the twin frozr the primary or to make the 3gb asus one the primary?