If you go through the guide at the first link, it will pretty much set you up with the basics to work on vectorization, and once done, you can look at what CoreLib does as a reference (just keep in mind it tries to squeeze all the performance for short lengths too, so the tail/head scalar handlers and dispatch can be high-effort, more so than you may care about). The point behind the way .NET does it is to have the same API exposed to external consumers as the one CoreLib uses itself, which is why I was surprised by your initial statement.

No offense taken, just clarifying, SIMD can seem daunting especially if you look at intrinsics in C/C++, and I hope the approach in C# will popularize it. Good luck with your experiments!