Do you have a LS1 radiator? I would love a picture myself, but don't have one.
The expansion tank connects to the radiator neck at the top nipple and the head vapor tubes (plumbed through the throttle body) connect to the nipple on the radiator neck below the expansion connection.
Unable to use WS6 radiator and overflow tank as damaged. Bought a cross flow rad off my local speed shop and managed to get coolant diagram faxed to me (remember faxes?) from a very helpful Lendrum & Hartman here in the UK. Found a overflow tank kicking about, which will do until I can afford a smarter one.