lengthing my driveshaft, got a question

[big83chevy4x4]

i need to know how much compression i should leave and still have plenty of droop.

i have 4" rancho springs and its 4.75" from the spring plate to the bumpstop. i was thinking 1" but i don't think thats enough.

id like to get this done tonight.

 

[84_Chevy_K10]

I'd say 1.5" left for it to collapse.

 

[big83chevy4x4]

ok thanks, now back to work i go.