Ls swap coolant system help

[sherm6413]

Ive searched threads and cannot find a specific answer I'm looking for. Its a 2003 5.3 in a 69 swb. just finished installing harness from bp, ls motor, and harness for truck from aaw, all is well, mostly, as it starts up runs fine has plenty of fuel and oil pressure. My problem is my radiator overflow starts pouring out antifreeze once it gets up temp around 190 and yes my fan is kicking on like its supposed to be. Do I need an overflow tank or "surge" tank as ive read about? My radiator is a crossflow from speedway. Should I just plug my overflow or add a tank it can blow in to? Help please