Rail Alignment without an optic?

[Wes225]

I recently bought as Troy VTAC Alpha rail and I'm slightly lost at what I could do to align the rail up with the upper receiver since I don't have a carry handle or long rail mounted optic to use to clamp them together for alignment when I attach the rail.

Any ideas?

 

[Double T]

It should have a slot for the gas tube to fit in, and then it can be lined up pretty easily and tightened up.