You should actually go ramp your truck until the spring is flat then measure what you need.
That's what I did.
![Thumbs Up :thumbs:](https://board.marlincrawler.com/Smileys/marlin/thumbs.gif)
I also gauged the angle that the spring was at when the bumpstop would contact the frame and mounted the bump stop frame bracket at that angle so it would meet the bumpstop flat against the bumpstop bracket making the most contact with the bumpstop. 8)