There’s also something from Snp 2.11 where it pops up in the context of the 5 cords of sensual pleasure.
Edit - apologies for the very short reply above, as I was on my phone.
There was a very brief discussion about this at - Interpreting the first Jhana
Since that time, I’ve had the opportunity to look at some of the MA usages, which suggest interchangeability between these terms. In the MA parallels to MN 19 and MN 20, we have 念 (saṅkappa) popping up where the Pali texts have vitakka.
What strikes me about these texts is that where the context is meditation and the concern is with sensual desire, ill-will and cruelty, the terms are saṅkappa and vitakka are synonymous. We can see this play out in AN 4.35 -
So yaṃ vitakkaṃ ākaṅkhati vitakketuṃ taṃ vitakkaṃ vitakketi, yaṃ vitakkaṃ nākaṅkhati vitakketuṃ na taṃ vitakkaṃ vitakketi; yaṃ saṅkappaṃ ākaṅkhati saṅkappetuṃ taṃ saṅkappaṃ saṅkappeti, yaṃ saṅkappaṃ nākaṅkhati saṅkappetuṃ na taṃ saṅkappaṃ saṅkappeti. Iti cetovasippatto hoti vitakkapathe.
He thinks whatever he wants to think and does not think what he does not want to think; he intends whatever he wants to intend and does not intend what he does not want to intend; thus he has attained to mental mastery over the ways of thought.