New suspension for K20

[California gold 68]

This week I'll finally have the money to start my project. The truck consists of 1968 C20 Custom Cab sheet metal resting on a 1977 3/4T 4x4 chassis. The first thing that will be going is the old suspension. New greaseable bushings for the front and rear, 4'' lift springs for the front with HD shackles and a steering box reinforcement kit all from ORD. My question is...... do I go with a shackle flip in the back or get new lift springs? I'm concerned I might lose the weight carrying capacity if I go with new springs. Cons or Pros??? Thanks in advance!