Ok, after looking at these pictures myself, the photos seem to skew how they really look. In person, they seem to have more arch, which is why I'm questioning.
They are supposedly 6" Pro Comp springs. However, I have 6" springs under my Crew Cab and Suburban, and these seem to have as much arch as the 8" springs under another rig. Of course, no weight of a motor makes a difference, but the guy I got the truck from also said that the front always seemed to sit a bit higher even when a motor was in it, and with 6" rear blocks.
It's alot like the "big Crew Cab". It had a 6" lift we were told, but always sat higher in the front. When I put an 8" lift under another rig, the front sat the same as the "big crew cab". The springs were pretty much the same.
I have another 8" all spring lift I was going to put onto a frame. If the fronts are the same, I'll just put the 8" rear under this frame and be done.