The Model 2A/2B/2C shares MOST of the same harness as the Model 3
Audio, Video, Digital IO and Analog IO are all the same (though Connector numbers are different foe each variant of the hardware).
The biggest difference is the power connectors.
Model 2 uses three 11-pin connectors with 5V and Ground, while Model 3 has only one of these connector, plus it also has a large connector with 3.3V, 5V and Ground.
Model 2 also have a 12V fan that is powered by a 2-pin molex connector
Model 3 also has BOTH a 5-pin video header and a VGA connector (not VGA Resolution it's still 24KHz RGB), while Model 2 ONLY has the 5-pin header.
Model 3 has a 12V fan that has an internal modex connector but power is routed through a 3-pin connector on the filter-board
So if you want to run Model 2 in a blast.
1. Start with a Model 3 Harness
2. you may or may not need to adapt the Video connector (unsure which connector the harness uses).
3. you then also need to ADD 2 additional 11-pin 5V/Ground power connectors.
4. You will need to adapt to the Model 2 fan connector
Filter-board Pinouts can be seen here:
https://www.arcade-projects.com/threads/sega-model-2-and-model-3-filter-board-pinouts.1121/