I've done a lot of digging through archives for reference photos of the bumper markings for my own truck, but there's unfortunately not a whole lot of information or good reference imagery out there, I can share what I have learned, though. Buckle in for a long post, as I've learned things during the course of typing this out that I can share.
As others have said, the unit marking format is standard across most, if not all types of US military vehicles and it probably hasn't changed since the 1980s, it's the same used for every other vehicle from deuces to MBTs so it should be pretty well documented, but i can't quite wrap my head around it myself.
Here's a rough guide that might help you. Pick a unit and follow the format and you should be fine.
For actually painting them, it seems like there was a varying standard but I couldn't find out if there was any kind of logic behind it. The two main types of painted markings are like this.
- Stencilled directly onto the bumpers/tailgate
- Stencilled with the tan rectangle behind
Here are some stills from a video of REFORGER 1987
(and here's the video), showing an M1008 with the tan rectangles and an M1009 without the rectangles in the same convoy, so either type is accurate for the mid/late 80s.
It's possible that this was just an overlap as they were changing from one style to the other, but the tan rectangles were used on other vehicles as far back as 1985, and they were still painting some CUCV markings without rectangles into the 2000s, so it's hard to say.
As for the marking locations, the markings on the front are always just left/right of the bumper as there's no other space, but the rear markings are sometimes on the tailgate, and sometimes on the bumper. Again, there doesn't seem to be any kind of set standard. Door markings seem to be uncommon outside of Military Police 1009s, I had a picture of one but can't seem to find it right now. Also, tire pressure markings on each wheelarch, I've seen them with or without tan background squares. There are a few other decals you can buy like the warning for the M1009 tailgate rear glass and various warnings about not standing near radio antennas whilst they're live, but I can't find any reference images of those in use.
Also remember the black star where the license plate goes, front and rear. I'm not quite sure where it's meant to go on the rear of the M1009, possibly to the left of the license plate cutout in the bumper.
Also worth noting is that in a lot of cases, the bumper, brush guard, and grille/light surrounds are painted solid green and are not camouflaged.
For the delineator squares, they're not a 1980s feature. The earliest evidence I can find of them being used is during REFORGER 90. If anyone can find visual evidence to prove me wrong then please do, as by my own judgement the delineators on my 1008 spoil the 1980s look I'm aiming for.
The video above shows vehicles with red tape strips and chevrons used in similar locations to the delineator squares. I can't get a good screengrab from the video but here's an M1009 in a junkyard with the same kind of chevron. I guess this was just what they were doing before the delineators were introduced.
Red tape strips and warning triangles also seem to have been used on other vehicles, here's an M1008 during REFORGER 88, note the strips on the bumper.
I have a whole bunch of pictures of other vehicles on REFORGER exercises with similar red tape markings, though the red strips on the bumper and chevrons at the corners seem to be the most common locations.
Markings aren't particuarily well documented, and I'm not claiming what I know to be the hard facts, but it's just what I've learned from my own research.
Hopefully this helps you or someone else.