The aftermarket system that Bill references may still be available from CPP or Brothers. However, I believe they are closer to $900 now. I had some experience with one and after many attempts to get it to perform correctly I sent it on it's way. It's unlikely that you will find a factory system. I have only seen a couple of them which were on high end trucks and the owners weren't giving them up. I have had success with installing the Toyota conversion on TF trucks. They are now becoming scarce and pricy as well. The box that is used is from an 84-87 4x4 pickup and there was a limited number of them produced. I have the conversion on my 56 and it works great.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine