I looked at about 10 Chevrolets today (C15A to C60L), only one had a hole similar to the one shown in post 12 and that hole looked as if it might have been a modification, not on production.
The first photo shows the only crossmember with a hole in the given location. You can see that the winch blocks anything passing through the hole.
The second photo is of a C60S tipper. The transfer case mounted PTO can be seen through the winch hole in the crossmember.
The third photo is of a typical crossmember in the group checked today.
The fourth photo is the same truck as the third photo, taken from below the frame. Again, the upper shaft of the transfer case can be seen in the opening of the crossmember (no PTO, it is a single speed case). The location where a transmission mounted PTO would be fitted can be seen just to the right of the muffler. Although the smaller hole shown in post #12 is roughly in line with the transmission PTO, it seems a little unlikely that a shaft from the PTO would be angled up that high to drive a pump but I do not have a water bowser to compare this to.
