I think your brake rod is original. My '49 1/2-ton is exactly like yours. It's a two-piece rod with a curved yoke in the middle. The replacement part is very expensive, for reasons I don't understand. It would be easy to make your own from a couple sections of all-thread and a hack saw (if the original look is not important to you). The spring attaches to the center yoke and then backward to the frame cross-member.