So far as I can determine, the above dates from the Vietnam Era. Latter phases of the Korean War at the very earliest. Every so often a cigarette lighter - usually a "Zippo" - will turn up with the "psalm" engraved on it. You're close, but it actually goes:
"Yea, though I walk through the valley of the shadow of death I shall fear no evil . . . 'cuz I'm the evilest M***** F***** in the valley!"
The term "grunt", of course, is military slang; first used by marines in the late 1950's or early 1960's to refer to or address "03's" (marines with infantry MOS's). The army later adopted the term during the Vietnam War.
In the 1970's, a private firm offered t-shirts featuring a cartoon of the stereotypical marine - muscle-bound, dirty, unshaven, blood-shot eyes and in full combat gear - superimposed on the "psalm" and strategically-positioned so as to blot out "M***** F*****".
They were advertised in Leatherneck Magazine for months and I'm told they sold like hot cakes. (Before you ask. No . . . that's one deal I missed out on.)