What you're experiencing isn't an issue with the Legend product that you're installing. All of our components are CNC machined and held within tolerances down to .003" of an inch so everything is very consistent when it comes to assembled lengths.
The issue that you're running into isn't that uncommon and it is due to inconsistencies in the welded components of the rear subframe assembly and can also be contributed to the age and miles on the bike along with how it's been loaded and ridden. We have even seen it on brand new bikes that we're test fitting products on. In either case, it is not uncommon to see an 1/8" to 3/16" difference between the left and right side mounting points. It's something that isn't apparent with the stock shocks or any other shocks with rubber bushings.
We suggest removing and installing what appears to be the longer of the two sides first. Then, when you go to mount the other shock it will generally require letting the jack down and putting some weight on the tire to get the mounting holes to line up.
Please email firstname.lastname@example.org if you have any questions.