Actually all M1008's are open carriers. M1028's and M1031's are where you find the Trac-Locs but not all of them have it. ALL CUCV M1008, 1028 and 1031's had 4.56 gears when they left the GM plants.
4.10 gears means it has been regeared or replaced by someone, somewhere. I just wasn't sure if you actually looked at the gears first. But I'd be more worried that someone swapped in used axles with 200K+ miles to get the low mile 4.56 axles for their truck. How well do you know the history?