There was a guy on STD who had fabricated a set of plates with the appropriate fittings to test the oil cooler. It had an air fitting with a regulator on the oil outlet side, with the oil inlet side blocked off and short plastic hoses on both the coolant inlet and outlet. You needed to assemble the oil cooler first, then clamp the ends in place (otherwise, the ends will separate when air's applied) and put the ends of the plastic hoses in cups of water. Then, apply air to the oil side...when I did it, I used the regulator to keep the pressure around 60 to 65 psi (the highest my oil pressure's gotten). If you don't get any air bubbles coming out of the coolant hoses, you're golden
Unfortunately, I don't think the guy who had made the plates made the switch over to OB...or, if he did, he's under a different screen name now. I have a picture of the rig in action
here, and if anyone wants to try and recreate it, I traced out both plates and could post the specs...