it looks okay like that, but it also looks as if they bondo'd over the body lines on the bed. i think if they hadn't done that it would look much worse.
in your case, i think you may have some issues of the mounts lining up, but its worth a try.
i personally have a 2nd gen cab with a 3rd gen bed and it looks decent...the body lines dont line up perfect, but who cares.