PY and Ames both carry replacement A/C Delco socks and pre-assembled socks on their complete sending units. For '66 the stock pickup tube is 5/16" - the replacement is 3/8" but it works fine. There is some difference in the sending units between A/C and non-A/C cars so make sure you get the correct one for your application.
Tim
http://kurtspontiac.homestead.com/TimSimpson66GTO.html