Here is mine, it is a '62 body on a '73 frame. I cut the '62 cab mounts off the original frame, and re-used them on the new one. I also cut the front few inches of the frame rails off and spliced them into the '73. The front bumper wouldn't fit correctly on the new frame. The biggest headache is the frame rails kick up under the back of the cab, so you need to raise the cab, or channel the back of it to sit over the frame rails.
In the end it seemed like an easy way to get disk brakes, power steering, and newer parts.
There are some pictures in this post that show the bottom of the cab.
http://67-72chevytrucks.com/vboard/s...0&postcount=48