Ok as I read your post it's all coming back to me now. I apologize it's been well over a year since I did this. But don't worry I'm fixun to give you the complete lowdown.
Yes, HD does not mention a lot of things. I went thru the same stuff you are and had to search all this stuff down back then but I had forgotten it.
Originally the "only" reason the sig relo kit was sold was as an "additional" kit to the saddlebag bracket kit. HD never envisioned that someone might want to just buy the relo kit by itself or inadvertently buy it first instead of after the saddlebag bracket kit.
So to make a long story short, you've probably noticed that the old relo fender backet bolt is smaller and more puny lookin than the forward bracket bolt. Well it's not recommended for mounting bags. To do that you need a stiffer bolt and to screw that larger bolt in you need interior fender bracket inserts that have the larger theads in them.
I had to buy this kit but had forgotten about it. " It " has the cosmetic hole cover included in this kit.
It's called the rigid sideplate mounting kit. They have the threads in them that holds heavier rear saddlebag rated attachment bolts.
It's HD part #53975-06 comes with the plug, better brackets for bags and hardware.
I've attached the HD PDF file of it. (edit the PDF must be too large it won't attach, let me see if I can find a link online so you can view what you would be getting)
This can be bought locally or at
53975-06 | New Castle Harley-Davidson
I bought the above and it's a better application for bags.
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If you think you don't need the heavier saddlebag bracket kit, you can buy only the hole plug. It's HD Part #56239-93
can be bought locally OR online at,
HOLE PLUG, 56239-93, HOLE PLUG
for a couple of bucks and shipping.