Think about it logically...
The rear axle on a leaf-sprung setup will almost always have the hanger at the front and the shackle at the rear. As the suspension cycles the spring will flatten and then re-arc repeatedly. And when it flattens the shackle will move rearward, then when it re-arcs as the spring is unloaded the shackle will swing back forward. Obviously that's because the elliptical spring elongates when it is compressed and becomes less and less elliptical, and closer and closer to a straight line.
Well if you watch the forward half of the springpack, you will notice that the axle arcs along a path determined by the radius from the axle perch to the spring eye bushing at the hanger. When compressed, the forward half of the spring hinges on the eye bolt and arcs rearward as it travels upward.
You need your link to mirror this arc path as it cycles.
Short answer....
Since automakers don't want the driveshaft telescopic section to have to endure endless slipping on collapse and extension while you hit every little bump in the road for hundreds of thousands of miles, they work to ensure that the driveshaft will also mirror this axle arc path as well.
So...
IF the truck suspension is largely unmodified, then the driveshaft should be a good angle gauge for you as a general rule of thumb.
And if you just want it to bind up..... run the links nearly horizontal on a high arch springpack, and run them up a mile long like most guys do. That way the springpack must bind just to cycle, and on top of that, when you actually need them to control wrap they will just deflect because they're too long to be useful.
:hehe:
