Camaros with sixes aren't that unusual, but as for an RS...
I have only seen 1 1967 RS with a six; convertible. I also have only seen 1 1968 Camaro RS with a six; again a convertible. That one was in Wiliamsburg VA back in '87. It had a 250, Custom interior, a console with a 3-speed manual (had a 3-speed shift map, rare). The car was black with a white top & nose stripes, plus white interior. Did you know that you could also get 4-speeds with sixes on 1st gen Camaros from the factory?
Yup, the sixes have surprisingly good bottom end torque, especially when you consider the smaller displacement. They run out of steam at higher revs due to carburation, manifolding, mild camshaft specs...