If I remember correctly, the 1958 and later cast iron PG has the PRNDL gear positions. I think that change was made to eliminate the possibility of accidently shifting into reverse when down-shifting to manual Low. The iron Powerglide with a V8 in front of it can be broken-- bring the engine up to 1500-1800 RPM in neutral, pull the shifter to Drive, press on the accelerator and the planetary gear set will shed its teeth. But I understand the '59 and later Turboglides would stand up to that- at least according to Chevrolet at the time.
Harvester
