I work at The Forge Makerspace in Greensboro, NC. I'm one of the heads of the laser cutter department. Our 50W laser has a red reference laser which can be quite helpful, but it left a bit to be desired, especially when we put a metal honeycomb under the workpiece. It can be really hard to determine if the workpiece is aligned to right angles which can sometimes be a big problem.

I developed this bracket which holds two "Red Line Laser Module 5mW 650nm Focus Adjustable Laser Head 5V Industrial Grade" which I ordered from ebay. (http://www.ebay.com/itm/281725342189) The bracket is made to guarantee that the centers of the two line lasers are exactly perpendicular to the shaft which houses the lens of the cutting laser. The bracket itself is kept square by slotting into the metal bracket to which the cutting head is anchored. Once you get the lasers focussed and adjusted (I used a bit of hot glue to immobilize the lenses once I got them into focus) then the lines should meet at the point where the cutting laser hits. Even better, if you leave the existing spot reference laser in addition to these new lasers, you should be able to determine that you're at the correct focus depth by seeing when the spot meets the crosshairs.

In addition to printing the bracket, you will need two of the red line laser modules I referenced above which will need to be spliced into the same wire that powers the spot reference laser. You will also need two screws and two nuts. Either 4-40 or M3 should work with this design.