64" springs in a 72 Blazer

[OLDCHEV4X4]

I want to put 64" rear springs from a 88-98 Chevy 2500, on the rear of my 72 Blazer. Anybody have any experience doing this? I also want to do the shackle flip.
I got the springs and the front hanger off the 95ish chevy. They are 4/1 and I am gonna remove the 1 (over load). I have them all apart and am wire brushing them and painting. Have new bushings, stock shackle, center bolts (they were metric) and am trying to get the correct wear pads. The spring shop sent me 3 different kinds and all of them were incorrect. Mine are square with a 9/16 nub.

Anyway, how many leaves should I run? Should I find a 5/1 pack?
How far foreward, or backward do I have to move the hangers? It looks like a body mount is gonna be in the way of the front hanger. I want a 20-30 degree angle back for the rear shackle. The rear cross member might need to be relocated.

The 95 spring hanger will have to be spaced out to match the stock front hanger. I dont have a exact measurement yet, but looks like about a 1/2 inch.

I want to keep the axle in the exact same location and have the same 2.5" lift.

Soooo, does anybody have any tech to post up?? Some pictures would be even better.