This is one of those situations where I probably shouldn't post because I risk insulting or angering some. That is certainly not my intent. So here goes:
Everyone reading this except for the spammers and bots is a woodworker of some sort. We make jigs and use tools with all sorts of capabilities and the results posted here are proudly posted, commented on, and admired.
If you don't want to use a level, or a straight edge, to align your rails, rather than buying an aftermarket jig to do so, why don't you spend a couple minutes in the morning over a cup of coffee and look at the situation and figure out how to take a piece of stable material and route a groove that will fit the raised portion of the rails and align them so that the screws can be tightened or come up with something similar. Isn't this the type of stuff we all purchased our tools to do?
Again, sorry for the forcefulness of my post. No harm intended.
Peter
Peter