I've done the same swap in reverse, that is from a '59 car to a '62 truck.
The differences are as follows:
1- The truck 223 uses the single front mount, while the car uses two side mounts. My truck-specific mount bolted right up to the passenger car block.
2- Truck water pumps are a different shape than the passenger car models, and use an extra spacer on the fan to clear the single front mount. You may be fine using the truck water pump, albeit minus the spacer. I'd suggest you compare the two to make sure. Check the clearance between the fan and rad.
3- Trucks use a different bellhousing, with two mounting ears on either side. You'll need a passenger car bellhousing.
4- Trucks and passenger cars use different size clutch discs, with different spline counts. These will need to be swapped. I don't recall if the flywheels needed to be swapped.
So, if your '57 still has the 223, keep it until the swap is complete. Having the two complete engines side by side would be helpful for comparison purposes. You may also want to keep the passenger car cylinder head. I've heard rumours that they have a higher compression ratio than the truck heads. Good luck!
~Jason