I can create a valid signature RSZ value with only the public key,
As far as I can tell you can not do that but I would love to learn something new. Here is a random public key, please prove me wrong:
030A6C83D64CE220CE007A980A4E789DFB81FC4757921D2E69266156DA8E6D306C
I am writing here because I do not know how to make a raw transaction in reverse.
You can't. As I said z is a hash produced using the transaction and since hashes are not reversible you can't first compute a favorable z then come up with a transaction.