I will give this a shot, but I am no expert on the task force series and I am going from memory for the most part:
Since the frame was stamped, pretty sure this is a second generation. They did not stamp the first series truck frames.
1954 had a closed driveshaft and the 55 first generation had an open driveshaft.
What type of front engine mount did it have. The early years used a two bolt through the timing cover and the later engines used a side mount with a single hole through the cross member. Not really sure when this change was made.
The second series did not have a full length running board so it will only have one support behind the cab, the first series had 3 supports on each side.
The first series has a shock tower mounted on the frame, the second series does not (going from memory)
The emergency brake on the first series had a horizontal shaft/lever that went behind the transmission, the second series did not.
The battery box for the first series is located on the frame and on the firewall of the second series.
The cross member at the rear bed is arched on the first series and semi flat on the second series.
The transmission cross members are different too.
The front spring perches are of different shape etc.
Just looking at the frame pictures that longbox posted really shows the characteristics of the two frames, compare these pictures to what you have.
First series Second series
