It looks like a No. 6 or 6A, but the numbers from all of the forged plow beams will tell the story as to what exactly it is.
Parts might be a little tough, but if you simply want to play with the plow it's best to take a good look at the bottoms for worn or broken parts.
I've got quite a few plow parts should you need some (assuming you buy the plow). My phone is 573 768 4092
Tyler in Illinois