They make whats called a 506 gearbox its a remake of a stock later modle gearbox. You can make your own. You just have to watch out for gearbx location. some are front some are rear steer. The 57 is rear(meaning the gear box is behind the steering assembly. Most late modle cars are front meaning the gear box in ahead of the steering assembly. I'm not in the shop now but will look in the morning and get some parts store names if you want them.
I think Danchuck is one that carries the gearbox you are looking for.