Diamond T & Ward La-France in the Swiss Army

[zemsi]

After the war the Swiss Army acquired quite a bunch of Ward La-France and Diamond T Wreckers. These were used for tank recovery and on airfields.

Unfortunately, all these wreckers had the same manufacturing year stated on their "Swiss" building plate. Here are some wreckers I know of:

Ward LaFrance (2nd number is the chassis number)
1943, 535364, M1A1 Model 1000 Series 5
1943, 422090, M1 Model 1000 Series 2
1943, 545315, M1A1 Model 1000 Series 5
1943, 434370, M1 Model 1000 Series 4

Kenworth
1943, 52287, Model 570 (1941)

Diamond T969
1943, 969B0005
1943, 969A0988

Does anybody know how/where I can source these actual building dates (month/year)?

Attached are some pics.

Thanks very much
Chris