NAPA may have a fluid-change "kit" which includes a filter. It IS ST ("Super Turbine") -300. The reason certain books call it PowerGlide is because they don't know the difference and "make it up as they go along". I'd be willing to wager it's not a Pontiac factory manual that refers to it as PG, but Haynes or Chilton or something like that. The '65 Impala mentioned WAS a PG. SOME of the 6-cylinder cars (not the OHC stuff, as far as I've ever seen) did use PG in the Pontiac. I've seen at least two in '64 or '65 Tempests with the 215 6.
If you can't find the parts you need, I MAY know a transmission supply guy that can come up with them. He did for us about 4 years ago.
