Head, torso and arms: 2003 MCC Leatherneck
Waist and legs: 2001 Gung-Ho
Helmet: 2000 Ambush
Backpack: Urban 6 Pack Alley-Viper
M-16/M203: Marauder Inc
I always had a soft spot for Grunt. He's the backbone of G.I. Joe. The infantryman.
Unfortunately, his figures haven't really left a very positive impression on me. The v1 is very outdated and has an ugly head, the v2 is just a tan repaint, the v3... the less said about it, the better... the new sculpt figures don't fit in my collection and the Comic Pack version wears a very issue-specific maroon costume. So I pretty much had to make my own.
Since the 2001/MCC Leatherneck looked, well, nothing like Leatherneck, he was pretty much an ideal base. The pants didn't really work for a standard infantryman, so I switched them with the pants from the 2001 Gung-Ho.
The gear was obvious. My Leatherneck had no helmet so he borrowed it from the 2000 Ambush (it didn't even fit well on that head anyway). The backpack seemed like a more nicely-scaled version of the original Grunt's backpack, and I just had to give him THE best M-16 ever made.
It's simple, it's excessively LBC-tastic, but I don't care, it works really well as Grunt.
And notice how in his third picture, I've posed him like the original Grunt's card art.