First, I guess I missed the fact that these springs were ordered without the OP ever seeing/owning the rig. I can't even fathom the idea of buying custom springs for a vehicle that wasn't sitting in my driveway.
Second, since none of this info has been supplied by Alcan so it can't be verified, I am really finding it HARD to believe Alcan would make a set of springs without knowing the weight load of the rear axle (since rear springs were being made). Total weight do NOT tell you the load of one axle, period. My Ram, with the FWC, surprised the heck out of me when I got front and rear axle weights and the FRONT weighed 500 lbs. more! I would have lost money on that bet. Since adding some items, I had it re-weighed and am sitting at almost a 50/50 split (rear is 40 lbs. more). Again, had I just gave them a total weight, these springs would have never been close.
Since we will never get both sides of this story, I really don't know what to say. I do believe that anytime you are going to modify any rig, you need to do your homework first. If you don't know about something (in this case how to measure for custom springs), you research, research, research. It took me 3 months of research, talking to suspension and spring companies and such before I made the choice to get springs made. My old Cherokee, I spent a year researching and buying parts until I had everything I needed for my needs and anyone who has traveled with me, knows that rig worked great! It did not happen by chance.