Preview
"Books and journals want (2a), not ((2)a)."
But there is no (2a) in the text, so every time the reader sees a cross-reference, he or she has to reconstruct it. (2b) is even more work, because the two elements aren't on the same line …
The (2)a you're trying for you is already easier to interpret; but I think I'd change the approach and go for something like:
2 strong past forms
2a. I painted last week.
2b. I applied last week.