The entire rear sight doesn't need to be changed. However, the sight knobs do. Many of the WCE marked Chinese made knobs won't hold zero, and should be replaced(the flat springs may be soft). Garand knobs will work, and may be easier and cheaper to find. Just don't put on more WCE marked knobs as they may be off a Polytech/Norinco.
See if the trigger and hammer have numbers and letters on them. The original Chinese made trigger and hammer will not be marked, and are often soft. Replace with USGI parts, and again Garand parts will work. However, from the mix of colors in that TG, grey and black, I'm guessing that someone has already done that.
I've got 3 Polytechs, one is a heel marked. I've done all of these modes to mine. I had issues with some of them, so did all of them to prevent more problems.