I put a crate 350 in a customers truck several years ago, after about 6 months it came back in with lifter noise. Nothing bad, sounded just like one lifter was a little weak. I ran the rockers 3 or 4 times and just couldn't get it to go away. Just as I was about ready to throw a whole set of lifters in, I thought I'd try one last thing. The noise turned out to be the fuel pump, which had also been new when I put the engine in.