Problem is, I cannot find a single "RSZ tool" that can check for the sighash_flag then switch the z-value calculation algorithm accordingly.

With that; DYOR, I'll just leave you some references:

• https://static.learnmeabitcoin.com/diagrams/png/keys-signature-hash-types.png
• https://raghavsood.com/blog/2018/06/10/bitcoin-signature-types-sighash/