Alcan builds the leaf springs custom to your specifications. They already know the length that is required for different heights (kinda) for the 05+ Tacoma and probably for the 1st gens as well. You just need to specify the additional lift you want or have and what additional weight you will have on your truck that will affect the ride height. The springs are already built to have 1/2" additional height on the driver’s side to counter the gas tank weight.
I just called them and told them that I had a 6" Fabtech lift and wanted to change out the rear springs for a smoother ride and additional flex. I didn’t like the rear blocks and the add-a-leaf that I had before because of a stiff ride and it also sagged down. I did not have them add in extra weight to mine because I don't carry anything in the back on a daily basis and wanted the best ride for my everyday use. All I told them was a full size spare in the back and the occasional full load of camping gear.
The Alcan's definitely softened the ride and gave more flex to the rear. The biggest downside is that the back of my truck is roughly 1/2" lower than the front. When ordering that was one of my key points, that I wanted to level it out. Now I have two choices, add in a spacer or install the shackle flip to level it out again.
Another downside, they are not impervious to rust. The salt and mag chloride definitely broke down the paint and rust started within the first winter.
I went ahead and added the All-Pro
U-bolt flip along with the Alcan’s. Added more clearance under the axle and cleaned it up a bit. I used the stock bump stop by tapping the plate that came with the U-bolt flip. I quickly noticed that the bump stop was going to be far too short with the extra added space between the frame and the axle. I need to get a longer bump stop now.
All in all I am happy with the purchase but still require spending more money on the rear suspension.