I have a family friend that was in a very similar situation (adopted outside of their race, have had the time of their life raising their child from infant to preteen, only to find themselves in a situation where being "white talking to a black preteen about things they don't believe they're qualified to speak on); understandable, totally.
From what I heared from them, they did independent research on how to handle "hair" and other puberty-related issues I guess they didn't think about until it was the time to cross that bridge. Ultimately what they shared with me is they did their own research, but most importantly didn't treat the child any differently. What I mean to say is, they didn't treat their adoptive child of a difference race any different than one of their own race.
It sounds to me like it's just time to be a "Dad", not necessarily make it a huge deal about the race-difference. Do some research, which it sounds like you already did regarding certain products made for that demographic, but as a big picture to having the puberty talk, talk to your son like you would if he was your biological son. Explain the changes to expect while going through puberty, offer advice, what you went through personally, etc. He's part of your family, not a random child you're communicating with.
I certainly cannot give you advice on how your dynamic is with him, but generally speaking, just bring it up casually. Ask questions, potentially humorous to break the awkward ice you may be feeling. Something like "boy I wish I had that mustache when I was your age!" or something along those lines to get the convo started. Then ask if he needs any assistance with how to take care of his changes, and if they noticed anything you could help with. Only if that's the dynamic you have with him. Again, these talks are very personalized and only you really know when and how to do it. But I'd suggest going in with some knowledge, but allowing him to speak most of the time and then chiming in "oh I've read about that product, do you want to see if the store has that for you so you can try it?".
In summary, our family friend just kinda put the race aside, other than asking the preteen if he wanted to go to the store and pick out his own self-care products after they did their own research on what the norm is with self care products for his race. Treat him like you'd treat your own. Puberty talk is pretty individualized and although there are resources, blogs, books, etc. only you're going to know when the time is right to bring it up. Our friends thought they were going to offend when doing so, only to find out their adoptive child had already done his own research and couldn't wait to go to the store and pick out his own products. From my understanding it wasn't awkward, but an extremely positive experience that brought them closer together.
Hopefully this helps, even in the slightest, as I'm relying on a third-party experience and not my own. Best of luck!