Cold Case Radiators now offers these water temperature sensor units for those wanting to connect two radiator hoses, while getting the most accurate water temperature.

These are recommended when using a radiator that isn't specifically setup for an LS car. You can use the 1/4 inch NPT bung for your steam port. 
With this adapter, you can use your regular radiator, connect this adapter with 2 upper hoses and run your steam port.
Details:

• 32mm to 38mm Hose Adapter. 1.25 inch hose to 1.50 inch hose.