Be carefull about
oil line size. You can get them too big. -12 is 3/4" - Are ther any 3/4"
oil passages in your engine?
I'm not a fluid engineer, so I can't quote numbers for you. But think about this - What happens when you connect a fire hose to your garden hose spigot? Plenty of flow, no pressure.
My V-8 did fine with -12 lines; but not sure about your engine. If you get low pressure after your cooler install, that would probably be the reason. Either install a high volume pump, or try smaller lines. But I would think -10 would be minimum.
You can also get the lines too small. What happens when you connect a vacume line to the garden spigot? Lots of pressure, no flow.