hope you weren't offended by a lil ribbing my friend. you asked which way was up not which way to put it on It can go on both ways. I have found with the norc gas locks that put it on one way it needs shims at the back of the gas assembly, put it on the other way and often it tightens up perfectly requiring no shims. This is NOT the case with usgi gas locks... unfortunately.
Often a guy with a welded on flash hider has no choice but to shim a loose gas assembly, however , I'd say 90% of those guys that remove the flash hider have found that simply flipping it over and tightening it up solves the loose gas system issue. It's it a good idea to check gas port alignment anyways cuz ya never know.