Problems with Melling M-55 oil pumps

[callfarms]

I am finally trying to finish building a 383 sbc motor that I started about 5-7 years ago and I am about to install the new Melling M-55 oil pump and I googled M-55 and all these warnings came up that some M-55 pumps were made cheaper and to stay away from them. Can anyone tell me what to look for to tell if I have one of the bad ones. The pump has USA cast in it and a 21 also. Both of these are on the bottom cover. Maybe I should just toss this just to be safe. Any help would be appreciated.