I used a Cold Case LS Swap 'dual pass' radiator 'kit' (fans and shroud). It was a little costly at around $400. But I was willing to pay a little more to know it fit 'OK' without any modification. I was able to reuse the original stock retainers on the bottom and made the top mount from a sheet of aluminum from the hardware store.
IMG_3471 by
Tom Sherer, on Flickr
IMG_3472 by
Tom Sherer, on Flickr
IMG_3469 by
Tom Sherer, on Flickr
Any down side? I remember being annoyed there was no provision for the LS1's 'steam vent' or whatever that small set of lines from the heads are. Not a big deal to solve, but I expected the provision to be there. And, they did not include Pigtails for the fan wires. The fans come with wires with a certain female terminal, but they didn't include matching male pig tail to connect up to it, which I thought was stupid.
I also saw someone who picked up essentially the same parts, individually for almost $100 less than I paid. So, shop around if your need to squeeze a few more bucks off.