3.1 L oil filter nippel

I recntly removed the oil cooler, which was leaking from my 96 Lumina PD. I was able to obtain another 3.1 L engine for parts, and having some problem removing the nipple that the oil filter screws on to. It doesn't have a bolt as the oil cooler version has for removal from the engine block, anybody know how it can be removed? Is it a hex key or small socket drive handle on the inside? My 5.7 L Vortec uses hex keys, but I am not able to see into the nipple on this car.

just where is the oil cooler located

Memory and the shop manual diagrams both recall that its simply a threaded tube that has a hex collar that holds the entire cooler assembly against the block. That's more or less it, just pop the lines off and unbolt the tube. Not sure what size, maybe 15 or 18. You'll see it when you look, I'm sure.