Here's the text from the gunthings site.
Colt M16A1 Parts Set with NEW US made barrel. Our kits have the sight bases mounted and barrels parkerized, this saves you time and money (sight base is original forged Colt, barrel is not Colt). All parts in photo are included, the kits do not include the disconnector. Original Colt marked 30 rd. mag, Colt sling and cleaning rod with brushes is included. Excellent - like new condition. The M16 the way Stoner meant it to be, with the light weight barrel profile so the weapon is light yet possesses plenty of firepower.
Since the front sight installation is not the original factory job, it is very reasonable to believe that is the problem.
It is even more likely to be the problem given that the new install is on an unfinished rifle kit.
I don't know how they verify alignment, but building the rifle and shooting it is one way.