shackle question

[gmcman]

I've bought some used springs for a 6" lift on my '81 gmc 1/2 ton and was wondering if anyone can tell me if I should use the stock shackles on the front or change them to a little longer (how much?) and a little thicker? Thanks!!

 

[GNERGY]

I put an 8in. lift in my burb and I used the stock shackles.
Tarey