I have just created a 3D printed model for a laser alignment tool. This allows you to attach a laser scope from a pistol in the vertical position and use it to align your enlarger or large format camera standards.
The model is at thingiverse and can be downloaded and printed. There are also companies that will print models for you, but I don’t have any recommendations on them.
Once you have the part printed out you will need a laser sight for a pistol that clamps to an accessory rail. Make sure you get one which features adjustment screws to aim the laser. An inexpensive sight for an air-soft or pellet pistol will be fine. You can get a nice one for $17 at Walmart, or less online. You will also need a small piece of mirror, which you can get at the hardware store. you might want to have the sharp edges dressed to make it safer to handle.
Start by clamping the laser sight onto the dovetail rail with the laser pointing up. Leave enough of a gap to turn the laser on if the switch is on the back. The laser aperture should be approximately centered, but it doesn’t make too much difference if it’s not.
Note: avoid letting the beam hit you in the eye.
Raise the enlarger head close to the maximum height (it will be more accurate this way). Place the mirror on the negative stage. Remove the lens from the enlarger.
Place the alignment tool on the baseboard, or better yet the easel, and turn the laser on. Position it so the beam hits the mirror and reflects back down. Turn the alignment tool on the base board. If the beam is perpendicular to the base the reflected dot will stay in one spot. If it circles a spot as you rotate you will need to adjust the set screws on the sight. This is the hardest part, but it’s still pretty easy if you do it in several iterations. First find the center position of the circle the beam makes as you rotate the tool. Turn the set screws to bring the beam to that center spot. Keep rotating, adjusting and checking until the reflected beam hardly moves at all.
At this time you should adjust you negative stage or baseboard to make the beam reflects back on itself. If you can rotate the tool and the beam always reflects back into the hole it emerged from than the two planes are parallel and the laser is perpendicular to the tool.
You should also align the lens stage. This is easily done if you assume the front filter ring of the lens is aligned to the optics of the lens (probably a safe enough bet). Simply hold the mirror flush against the lens filter ring and adjust the stage as you did with the negative stage.