I attended an Adult Ed classes twenty odd years ago to make the blocks, but certainly in my area, Kent, these classes don’t seem to run anymore. At the class we used Natalie Bray.
Consequently I’ve used NB and also Winifred Aldrich in more recent times to redo my blocks. I find NB quite long winded and sometimes the explanation of why you’re doing it distracting, and like the bullet points of WA, but backed up with NB. Also as a fan of vintage patterns, NB has some classic designs, which in my opinion are a good basis for more modern designs.
For adapting blocks I have used Helen Joseph-Armstrong “Pattern MAking for Fashion Design. It’s an American book so still in imperial, but offers more design than with NB or WA. I don’t find her instructions for drawing the blocks as good as the other two.
I guess what I’m saying is I need a variety of ideas to learn and trial and error and lots of toiles!
Hope you find something to help you progress.