That waterneck is for use on a jetboat with a engine mounted waterpump, the large outlet goes to the large water conection to the water pump inlet and made it work very well with a thermostat. 

Also needed to make a closed cooling system work when you have a heat exchanger on the motor with anti-freeze in the block....

Keep it in the swap meet pile for sure...

Do you need another outlet for non water pump use?

GT

heres a few pis of the one on my rogers.  BBC but looks close

Rogers Hopeful, that thing is gorgeous 

The large hose shown going down to the right side of the engine goes to a factory style waterpump.....

GT

Thanks GT, we are accumulating a bunch of swap meet stuff, and will be posting later.

P.S. Sorry to disappoint you with the answer the "there is an Answer", I am currently working on a mathematical answer that hopefully will redeem me.