It is a 1957 according to the color of the motor cover. The '56 models were all one reddish color, the '57 was white on top and reddish on the sides like yours, and the '58 engines were reddish on top and white on the sides. Each year used a different reddish shade but they were all called Holiday Bronze.
You need the engine model number from the metal tag to veryify the year as long as someone did not play "pieces-parts" over the years.
I have all the 10s in the Johnson lineup from 55 to 58, and I have to say the 57 is my favourite.
Starting with the Evinrudes now, but the 57-58 Johnson lineup has a special place in my heart
I never thought about the weight before, I cant imagine its much though