LS overflow tank

[upon1]

Doing an LS swap on 55, with a champion rad. Is an overflow tank necessary or just leave the fluid an inch or so from the top?

[dsraven]

this is a pretty good write up on how the LS cooling system works, which is different that the old style small block stuff you may be more familiar with. there is quite a knowledge base on that site for LS engines as well as other stuff. it is a 4x4 site but they also talk about related things like tube notching, building roll bars, suspension stuff etc. good info to know either way.
I always recommend an overflow tank. that's just me though.

http://www.pirate4x4.com/tech/billavista/Cooling/