shackle angle

[Tex]

i plan to install 63 inch rear springs, i plan to bolt on the front hangers where i want them to place the axle where i want it, my question whats the best way to determain where to bolt the rear hanger so my shackel angle is right the first time? without a bunch of trial and error leading to a bunch of unwanted holes in the frame i thought clamping  them to check with weght and adjust i just want to be safe and not hurt myself and hoping mabye there was a science to it

[four_by_ken]

Clamp them in place like you said and get the weight on it.  Should be slightly backwards lean.

Usually a good starting place with no weight is straight up and down.

[Boggen Joe]

About a 30* angle I read somewhere