[Rich Biebel]

That is correct and all the cars that had 4 speeds and hydros had to switch to 3 speeds or powerglides back when the rules were changed.

4 speeds were only allowed in Corvettes and 4 speed automatics or hydros as we called them were out...

Powerglides were not very competitive until Marv Ripes developed his small converters for them...His car that was driven by John Barkley was the only fast p/g car during the era of the hydro equipped sedan deliveries...He must have used that car to develop the converters for p/g's...

This change was back around 1968 or 1969. To many bogus combinations that were never really assembly line production cars.

Some racers tried 3 speeds but they were tough to work with and were mostly used in 55 and 56 cars with 265's....that always had them...

Now the modern rules allow 3 speed automatics in cars that only had 2speeds....so that sounds like a '57 could get a metric 3 speed........I don't know about the 4 speed vs 3 speed manual trans issue...