Guys, this has been a very interesting conversation, but I want to identify something I thought was obvious way back when Boss posted it. On Boss's 3rd post (Jan 7) where he showed the close up photos of the fender. On the third photo down, you can actually see at the bottom of the filler rod, where it was welded and ground off, at the bottom. There is a little angled piece that is obvious weld that has been ground off, right above the nut holding the plate onto the fender. I'm sorry, but I'm not a great metal fabricator, but I could have done this cutoff job and welded in a piece of bent rod then ground it out smooth.
I submit to you, not so good welding job that you couldn't tell it had ever been welded, from my 65 Lo-boy that had a loader on it, and someone chopped off the seat bracked so the loader mount would work:

And after:

It would be a simple job. Also, I can assure you that it's HIGHLY unlikely that IH did this at the factory, or we would see MANY more of them, and would see an obvious part number difference, neither of which are there. As Rick said, the rest of the fender is stamped, and this is obviously a piece of rod welded to the fender. There's NO WAY that they would have stamped a fender, then taken the time and money to weld in a filler rod. They REALLY would not have cared about the access to the platform, or they would have done it back when the Lo-boys started production, along with all the other changes they made to actually build a Lo-Boy Cub tractor. Re-tooling the fast hitch, rotating the final drives and adding/utilizing the extra holes needed to make it work, etc. I'm certain they would have done the fender at the same time if it was important (or even a care) of theirs. The second fender that was posted by Chris D actually backs up this, as it's even cut more different, back at an angle. No, this is something that someone has done at home! Like I said, it's been a great conversation though.