The only thing I find on "Diamond T" is a touring car from about a century ago. Diamong Reo, on the other hand, does have a model from back in the '40s that looks a lot like that. But, the pic says '40s and does not say which out of the ten years it was. Second half of the '50, they went to dual headlights. And, during the war years, it was all concentrated on the "war effort". So, I would suggest putting it in a range of about '47 to '55.
The pick says '40s. Looking at the grill and headlights, it seems to be close. Only problem is that the same style could have spanned about 5 years. Even today... Look at a pic of a Freightliner Century and tell me what year it is...:smokin: