I just saw that dominate white and some white in the lobes and being a leghorn fan had to throw that out there.I would keep him, personally. Always love a quiet roo
From what I can tell, he has Mahogany and dominant white genes. The white is taking the place of all black.
I'm gonna guess he is RIR over white rock. I've seen RIRxWhite Leghorn and neither the males nor females turned out like him. And RIR over RIW makes the typical red sex link.
You'll probably never know for sure.
I did like the RSL F2 idea. I could go with that too.