I have a 1994 C3500HD. I bought a rebuilt 7.4 and can't figure out which oil cooler line goes the top of the radiator and which goes to the bottom of the radiator. There are two fittings at the block for the oil lines. One is flow out and the other is return. Sure would appreciate any help.

 

On mine, the line on top of the radiator goes to the back. The one from the bottom goes to the front. Not much traffic here. Have you already solved your problem?