This may be a long shot. When I build my M923A0, I plan a “foodtruck” from Troop Challenge FTX 2002. That truck had lots of MRE`s and hot food pan containers loaded but also boxes of Unitized Group Ration boxes. I remember had an UGR tray years ago but forgot to measure it. 
BTW Where is “Magic” Frenchy when you need it?
Don’t know the exact size, but the tray is about the size of a large casserole dish; maybe 9" x 13".
Larger boxes they come in.
Here is a YouTube video of them that may be helpful.
Thanks Gino! I think the pallet is 40x48? Then I have a way to guesstimate the size.
From “MIL-PRF-32004, PERFORMANCE SPECIFICATION: PACKAGING OF FOOD IN POLYMERIC TRAYS (23-MAY-1997)”
Looks like you’re entitled to a small margin of error… 
H.P.
I was pretty close with 9" x 13". 
This gets even better. Thanks guys! I just work in POL pails for my Stryker, next will be UGR boxes.
Indeed… Happy Birthday Gino !
H.P.
Thanks Frenchy.