The 41-46 cab is 1 1/2 “ longer as mentioned earlier, the firewall has the extra ledge supposedly for leg room. The cab is moved back on the frame 1 ½ “. The indentation on the firewall for the valve cover is the same 39-46. The hoods are different because they moved the cab. If you move the cab forward for the 40 you will have a firewall problem.
