I don't think you are concerned with the engine data plate...the engine has NOTHING to do with weather it is an A2 or an A3 as far as I know....I have owned my M109A3 for about 20 years and have seen many sinse. There should be a delivery date on the vehicle data plate. should read something like 02-65 (feb 65). At the top is should read something like M109A3 WO/W and a Serial number. The last M109A3 I looked at came from the depot at Toolie (sp?) Army Depot where it was having the gas fired heater, either injector, and a few other items installed. It was never completed and sold via DRMO. I believe it was a MO National Guard vehicle.
Has a D turbo, Sprag transfe case, 60 amp alternator. I also think its delivery date was in '68 or so. Several MWO tags on the door jamb.
It is important to note that these vehicles are OLD and have gone through many MWO's to upgrade and standardize. For example, if the xfer case broke (common with the sprag type), it was replaced with the air shift type. Speedo's and Tachs were also replaced as they broke so, Just because it has 600 miles on the odometer dosen't mean it really had that on it....compare it with the hour meter on the tach.