I made the same swap about a year ago. The 55's had a open drive line. The difference in the cars and truck are that the housing on the cars have an oval design to them while the truck pumpkin is round. The truck pumpkin is interchangable with the trucks from 55 through the mid 60's and are usually 3.90 gears.
In my application I used the 3.90 gears and an over drive transmission. This gives me a final drive in OD of 2.73 on the high way.
I also have the hauling capacity with the 3.90 gears.
Gotta love it.
Tom
