jacksun,
The holes for mounting the windlace channel on the 47 through early 49 are threaded. It's my understanding the late 49 through 54 windlace channels are welded in place.
It's possible to make your own windlace channels that resemble the 47 thru early 49; however, that could be quite a project.
I was able to find windlace channels for my 47 in the "Truck Parts Wanted" forum. They are out there and some are in pretty good shape too!
