best carberator for the stock slant 6

A super six is more expensive than that. At least $200 for an intake, air cleaner, and kickdown linkage + brackets. Then you'll need a decent carb. You can either get an unknown or reman carb or you can do the right thing and find a NOS carb for $200. Then you've got to get the good gaskets and either do the work yourself or have a machine shop resurface the manifolds. You'll also need a new accelerator cable while you're at it.

To the original poster...why don't you tell us what you want your car to do. Do you want horsepower or do you want gas mileage?

or you could just wait for someone to give away a supersix that they don't want anymore. I gave away 2 supersix engines not long ago because I changed to v8