Vintage Saab Two Stroke Early style E Brake arm upgrade

When Saab went to the later style rear brake assembly at serial #135,000 and up. (Appx 1963) they used an emergency brake apply arm that was actually too short and design, and didn’t have a notch to catch the brakes shoe. It makes this very hard to install everything and get to work properly. I’m guessing these failed immediately at the factory and a running change was implemented. Like I said in the video 1964 cars had the leader arm, but the Parts book does not show any change. It’s simply Saab modifying the part to make it actually work this time. 
So I would not recommend using the other other arm I’m afraid it would come disengage from the brakes shoe and you may have other issues The one side of this rear brake assembly had came apart at one point and had ruined the drum.