I have a 69 Cutlass with a TH400 and am wondering about a plugged connection on the PS top of my radiator. This is a aluminum replacement radiator. The trans cooler is in the radiator. I saw an engine compartment pic that had a hose connected to it but not enough of a view to see where it went.
thanks,
Steve

 

It's a universal radiator that can be used in cars that have a heater core return line to the radiator.

 

It's a universal fit tank. Starting mid 70s a lot of GM cars started routing the heater return hose to the cold side radiator tank vs the earlier practice of routing it to water pump suction. The idea was to reduce or eliminate an "objectionable" gurgle in the heater core.

Before the factory re-engineering, the dealer fix for the gurgle involved a brass tee in the lower radiator hose. Heater return was routed to that. The water pump fitting got a rubber cap like you find on a Dorman Products "Help!" aisle.

At least your new Al radiator has a threaded plug instead of a rubber cap.