The correct version of the M1 helmet is the Vietnam era style, lower profile helmet. Hope this is helpful.
If your looking for the Correct version here are the things to look for;
Curve of the Helmet, left is the 1970's M1, right is the WW2 version.
The seam around the bottom of the helmet is joined at the back, If you find one with the seam at the front its a WW2 version.
Your straps may vary and could have been repaired with a plastic rim for the strapping to fit to the inner helmet, its your choice to decide how authentic you want your build to be. here is an original inner with original strapping.