I think widefront has quite a few rare tractors. He has an SS (only seven made). CH (also only a few made). Spirit of 76. (Say 500 or less) smooth block center exhaust SC (200 or less made). I love his collection.
I have an airborne SI. The original war department manual shows less than 200 made.
I agree with gmccool. Dad has an 870 gas 8 speed open station. I think there were less than 150 of those made.
I like seeing the more odd/different variations