personally, i don't think you'd need to go very big at all... it's a 1600cc after all... in my case (1ggte) i'm going for something only as big as what i can fit... 550mm tank to tank...
you could save yourself a bucket as far as the install goes, if your handy with a mig welder... just get ahold of a few bends, some straight pipe, a hack saw, and some silicone joiners and clamps... along with a hole saw, and/or die grinder...