For those less inclined to build their own I thought I'd share a link with a truly remarkable unit from Adrel Electronika in Poland (photos below). The U.S. Spacemodeling team has used this the last few years to verify the quality of motors we purchase at the Internats. It's a small unit designed just to test model rocket motors. Portable, touch screen operated, runs on a 9 volt battery, data downloadable to excel. Pricey, but phenomenally well designed and easy to use.
A number of different load cells are also available for purchase for the Adrel, from low to high power capable. Like you, Bill, I had to incorporate the load cell into a test stand. The Aerocon website
gave very nice instructions how to build one.
Final note. No talk of model rocket motor test stands should be complete without a shout out to the late Art Rose, who for years produced the only commercially available hobby rocket motor test stands, which you can read about here.
They were from an earlier, more cumbersome, era of electronics but they worked, and Art made them available to those of us with very limited technical knowledge. Just another of the many ways Art advanced our hobby.