That is known as a steering knuckle. If you look here at the GM Parts catalog GM Listings you will see that they have one part number for 46 to 50 and another for 51 to 57. By the notes it is the same forging but the later setup has larger holes. If you used the 51 brake setup on the front, I think it would be fine. That is the year that they went to the Bendix style brakes.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!