Straight up and down is better. I used mine at an angle to get more travel up and down. That's the reason they'd be placed at an angle.
Your reinforcing plates will do what you want then to but the threaded rod you're using worries me. Even if its a grade 8 bolt cut down, I would think it may break easy from the welding. A piece of 3/4" thick wall tubing welded to your plate that the bolt could pass thru may be better.