Horses for courses, but block inlay appears to be your best bet. In my experience pre-radiusing works, but you will almost certainly need to sand a little once in place. Not an issue if you do it carefully.
It will be a challenge to route the block cavities with the frets on. If it were me, I would likely take frets out, do the inlays, radius and then refret. More work, but easier to get right.
All part of the process, so hope you can forgive yourself and enjoy the journey. Mistakes are what drives progress.