Well, the mystery is solved on the dimensions on my tailgate. I checked on the GM heritage site and the bed dimensions on a '46 pickup is 48-1/2" inside. So that matches with the tailgate I bought to replace mine. Other than the ~1" width difference (and all the dents in my original '51 tailgate) they look identical.
So I guess I'm posting up a '46 tailgate in nice condition for sale. Might be a tough sale as there probably aren't many pre-'46 pickups up here in Alaska. Pretty heavy and costly to ship down to the Lower '48.
On edit: Looking at it some more, it looks like it's actually a 47-51 tailgate that's been cut down to fit an earlier bed. The end pieces have been welded all around the perimeter at the skin and where the skin rolls around the top and bottom rail. The notch in the skin at each end of my original one isn't on it (probably cut off and welded over. There also appears to be an additional tube inserted inside the top rail to reinforce it (not there on the original tailgate remnants I have). It has the embossed block "CHEVROLET" lettering, where a 46 would have no lettering or a script style. Trying to stretch it back to the right dimensions to fit my '51 probably isn't going to happen.
