Hi, will definetly need some better pictures to comfirm, but it is not WW2 or Korean and is probably 70s or 80s.
That stamp says 30 I couldn't get a clear pic of it.
The liner looks to be late to post Vietnam war, i would say 1970s, the early to mid Vietnam war liners are more a brown colour and the later 1980s ones have detachable liner webbing and are not attached with A washers.
Thanks for that I was hoping it was around the Vietnam era.
You just need a nape strap and sweatband to complete it, it looks like it has had a repair to the webbing at some point, but i am sure it is period.
Very nice Firestone manufactured liner, I agree with Harry's comments regarding the era.