No pictures of what I built, sorry. Excellent sketch Phillip. Very close to what I built. I used three angle brackets rather than 4, for a simple 'tripod'. No wood base. I put a screw in each bracket with the head facing down on the baseboard. Two nuts on each screw, one above and one below the angle bracket. Once the laser pointer is held firmly in the bracket tripod (with two hose clamps), it was easy to adjust the screws until the laser pointer was exactly perpendicular to the baseboard. Put the assembly on any table and tape the laser pointer's on button down. This puts a dot on the ceiling. Spin the assembly slowly and the dot will make circles, because it will certainly not be at 90 degrees initially. Adjust the screws slightly until the circles on the ceiling get smaller, and smaller, until the circles become a single dot. Perfectly perpendicular.
Once perpendicular (took me about 5 minutes to get it exact), you simply have to place the assembly on your previously leveled baseboard and hold a mirror flat against the neg carrier (neg plane) and adjust your enlarger's leveling adjustments to perfectly align the baseboard with the neg plane. Do same for face of enlarger lens (lens plane).
Assuming your enlarger has leveling adjustments like my Omega D2V, you can easily align the neg, lens and baseboard planes. Buying the laser alignment tool, about $150 I think, would have been easy. My way costs about $4 plus the cost of a cheap laser pointer. (I already had one laying around.)
Works great. Hope this idea helps other people too. APUGers have helped me in so many areas.