Hi all! I read an article about the Asus RT-N15U router and saw that the router has hardware options. Here is a photo of the router that I have on hand. Perhaps this will help you complete the firmware.
board revision 1.10
main chip is BCM53125SKMMLG
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@tmomas - it appears you made the note the OP is referring to (about 8 years ago).
And @n0whereman - thanks for the screenshots and welcome to the community!
If it interests you: Applying for OpenWrt wiki account