I checked here:
http://www.radiomuseum.org/tubes/tube_6c6.html
http://www.radiomuseum.org/tubes/tube_310a.html#a
Neither is listed as a substitute for the other. So I'm going to say no.
http://www.radiomuseum.org/tubes/tube_6c6.html
http://www.radiomuseum.org/tubes/tube_310a.html#a
Neither is listed as a substitute for the other. So I'm going to say no.