Which heater hose is the return line? I'm installing stainless hoses, & in order for my heater to work properlly the return line with the heater valve must be hooked up to the correct location. is the nipple on the intake the return to the block or is the nipple on the waterpump the return? Thanks

water pump is the suction. comes out hot from the t-stat crossover area.

The bigger one is the return.

Usually it's a 5/8" feed and a 3/4" return on most small block applications (not always). If it attaches to the thermostat area it's the feed. If it attaches to the water pump it's the return.