Leaf springs and shackles

If I put a set of leaf spring shackles on the front part of the leaf springs along with the one's that are on the rear of the leaf springs how can I keep the rear end center of the rear wheel well and it not be able to shift front to back while in use ? Because I needed to replace the rear end in my 2003 GMC Sonoma SLS 4.3 V6 Vortec crew cab 4x4 and while jacking it up I noticed both ends of the leaf spring on the passenger side were completely broken off , so now I have to have leaf springs ! So I have a 2000 Chevy Blazer 4x4 4.3 V6 Vortec with the exact rear differential I need for my GMC , so I decided to just drop both rear ends at the leaf springs and swap them out , once I got the rear end from the Blazer installed in my truck I realized the leaf springs from the Blazer are 1 1/2" shorter than the ones from my truck , so it's not center and the tires are only 1/2" from touching the fenders due to it being shifted forward , how can I fix this problem and keep what I've got without having to buy and replace the leaf springs ? Any help or suggestions would be greatly appreciated because I'm getting very frustrated with this thing every single time I fix something on it or replace things that are considered every 3-4 yrs maintenance or replacing something else happens , I would do away with it but it's a good little truck and it's all I've got that is all mine lol thanks !