Dwight et al,
That's a beautiful diorama, isn't it? WOW. A lot more work and patience than I have in me!
Just a few comments on the M113 family itself though.
If I recall correctly (which I may not, help me out here Major if you read this), the M113A1 which was Diesel instead of Mogas, came out after Vietnam, so don't put any Diesel decals by the fuel filler.
Also, interior wall color should be white (gloss) with a dark green floor (worn through to aluminum with lots of grime). I don't think the light green interiors came out on the family M113 until the mid -70's, after Vietnam, though the M577 had that color inside.
Bench seats had green pads, crew seats black. The crews usually 'oiled' the camoufalge paint back then, so it would have a dark green semi gloss look to it. (I use Testors Model Master dark green with semi gloss over it... it matches what I remember pretty well).
The side 'skirts' tended to lose their paint and scratches of black (dark gray) rubber would show up on them. That would give the vehicle a nice weathered look.
Like I said, I'm going on memory here. If Major G. can take a look at this and either verify or correct me, that would be helpful. Another good reference is Squadron's Armor in Vietnam book.
Hope this helps!
Ron