I have no way to tell who you are to contact but I remember talking about it last week. You're right on the edge of this just going together, to the point that the ubolt system will probably make it a non issue. Here's a pic of my K5 with 2 rear shackle systems still on it:
The shackle flip has a small steel bar welded across the front to act as a shackle stop and the shackle mount that's in use has a simple steel bar welded to the tube to act as a shackle droop stop. The set of springs used with the flip system required a spreader bar to install so the arch or preload was a LOT more than your spring pack. Yours should come together fine once it's all together. As a start, tack weld your spring perches on at the stock angle. This generally sets the pinion about right for a cv driveshaft in a shackle flip suspension. After you load it and bounce it around you can drop it, grind the tacks and adjust if necessary.
Some more general info:
Alcan has nothing to do with these springs other than building them to our specs.
A 56" main leaf would be terrible in this system. Huge shackle angles are not desirable most of the time on our trucks, especially where ride quality is an important characteristic. I actually do the spring design work and the spring lengths are not a guess in any way. They're set deliberately but not around what seems popular. The shackle angles are set when the springs are flat and often look "wrong" when the spring is sitting with some arch.
I'd much prefer the tension shackle here too but we can't get a 6" lift with this spring length without a LOT of spring preload and not many people are able to deal with that so anything over 4" of lift gets a flip. With a 64" spring we can do a 6" lift without too much preload but even at that point you may have to flatten the leaves a little to get the shackle bolted up.
@rpcraft, we run the tension shackle up to 4" since they actually work a little better than the flip system in a couple ways and the install is simpler and cheaper without having to buy a flip kit.
If anyone has trouble with their springs, CALL US! They're a bit unconventional so a lot of the time what looks wrong is actually OK but sometimes things are messed up somewhere and there is no reason to put up with it.