[Uncle Bob]

Thanks for the questions, it helps (I hope) eliminate speculation from others later.

I haven't had time to do any dis-assembly yet and only part of a partial serial number is visible at the firewall foot. Once I get that removed I'll probably have to acid etch to bring up the whole number. The one that should be at the rear kick up is completely obscured by pitting. Yes the center member is riveted in as expected, and as mentioned there is no evidence that the forward K legs were ever there. Once I get the rad removed I'll take a pic of the front cross member. Like you guys, I've always believed the front should have been riveted. The thing that's made me wonder is that all 14 fastener sets are identical, and there are uniform spacers under the "feet" that attach to the bottom of the C channel. The side rails are pretty uniformly aged, and with the center member rivets looking "right" I doubt as many as 5 different "parents" are involved. The rear cross member could be a replacement (likely as the fasteners are hokey looking enough), and as it's cracked through one of the U bolt holes (not uncommon) will need to be replaced again with a nice one I've got on the shelf.

"Rarity" is of little concern to me or my thinking, I'm just curious to learn for learning's sake.

It's probably best to just let the reveal challenge slide.