[Racer Chris]

The trailing arms are pretty sturdy, and don't flex as much as the ads for the boxed kit would have you believe. With the big engine you run it might be worthwhile though, especially if you have other upgrades and run on very wide tires. Buying a pair of used arms and boxing them before installation seems like it might be a good idea. I wouldn't expect them to crack just because they weren't new. The photos look like there was a previous repair that failed maybe? I've never seen anything like that. The chassis crack is much more common. It's a good idea to reinforce the chassis/suspension mounting area.