I realize this post is about 8 years old but I hope you will receive this message.

I too, am looking at replacing the slim jim with a 700r4 and leaving the 394 in the car. I have a 63 Starfire. Did you have to modify the tunnel? What other mods did you make? Did it require new linkage or modifications to existing? Did it improve your gas mileage and if so by how much. Name, address and phone for person who did adaptor? Did you have to change the drive shaft? And any other good info?

 

I created your own thread in stead of resurrecting one that's 8 years old. Here is a good read, its a 64 but lists some vendors and gives you an idea:
https://classicoldsmobile.com/forums...-394-pics.html