Bolt holes will line up. That was the original intent with these trucks. The floor of the cab will accept either high or low hump cover. Main difference was the piece spot welded to the firewall.
63, if you have the 3 speed, either cover will work. Low hump was standard for the 3 speed and Powerglide transmissions. High hump was for the 4 speed, but will not be a problem with the other transmissions.
If you go with the High hump, you will have to specify you have that if ordering carpet or any other floor covering because it does make a difference for that.
