The cast iron case PG shift quadrant was P-N-D-L-R. I learned that the hard way one night while driving my girl friend's 55 Chevy 265 V8 and tried to pull it from Drive into Low gear for some full-throttle acceleration. OOPS! Reverse and full throttle at 35 MPH is NOT a good combination! Amazingly, that old PG survived! The TG shift pattern included "Gr" (grade retard) at the full right-hand end of the quadrant, a way of getting compression braking on a steep downhill grade.
There's nothing really wrong with a Powerglide trans, except that it has only two speeds- - - -"Too low and too high!" The 63-up aluminum case trans is a better choice, but lots of the old 1st. generation transmissions are still around and doing well. The filter is under a cover plate on the passenger's side of the case near the bellhousing, and that one does have a converter drain plug, so you can do a full fluid and filter change when servicing it.
Jerry
