The 57 transmission will be a cast-iron case Powerglide. It's heavy, and pretty obsolete. Getting one repaired would be a real hassle, so I wouldn't reccomend installing it, with all the modifications necessary to do so. If you can find a 62-64 aluminum-case Powerglide, it would be a better swap, but the drag racers and roundtrack racers have snapped up most of those transmissions. I don't think the later 3-speed automatic transmissions will bolt up to a 235 without some pretty extensive adapting. You might be better off staying with a standard trans, as the standard shift bellhousing will accept several more modern transmission options with a minimum of tweaking.
Jerry
