If the acceptance or delivery date is not on the data plate, the closest you'll may get is to look at the DLA contract number. The 7th and 8th characters are the date of the contract. Of course, contracts run over into new years and some contracts take years to fill but it's as close as you're likely to get.
In the FWIW catergory, the build date, if present, and the date imbeded in some serial number sequences reflects when the frame was designated for a particular model of truck, not the actual completion date. Some "low density" model frames were fabricated in batches and then used over a multi-year period.
Some trucks have a "delivery date", most don't. During some periods the year in which the frame was designated is part of the serial number.
Both the truck and trailer should have data plates with the weights. If not, the generic weight for an M35A2 is about 13K, empty. Add 5K or 10K. The generic empty weight of an M105 trailer is 2,700 pounds. Add 3K or 6K.
The amount of weight you add depends on whether you'll be loading them with the "new" lowered rating for both highway and off-road use or the "old" 5 ton and 3 ton "highway" rating.
What are the frame or data plate numbers for the truck?
I typed this ina hurry so I hope I got it right...
Lance