I bought an electronic automotive spin balancer back in the 80’s and was told by the guy who sold it to me that he increased the sensitivity of the unit a bit to balance smaller wheels. I never saw a calibration table, so I’m not certain if he really did anything. There are two modes for balancing on those machines. Dynamic and Static. I was told to use Static setting which is adequate for a Kart tire. I was very successful with the whole project and used it for 15 years. Since I had two karts, raced 5 classes per weekend, I had 12 to 16 tires to balance. It was extremely handy. I had a couple of adaptor shafts made with a straight taper to use a front wheel hub as the mounting spindle.
Have you tried using the unit you have access to? As I remember, the only data I had to enter was tire diameter and select “static”. The amount of weight to add is relative. It might indicate a number for wheel weight based on the assumption that a larger tire is being used. Once you establish your translation table of indicated weight vs actual weight required, you’ll be ok.
The big deal was getting the special spindle adaptor machined at the time.
