Can anyone tell me what section of Reg Z addresses the required preliminary disclosures for open ended, non RE secured products? (specifically, overdraft protection accounts which are unsecured)

I know of no "preliminary" disclosure requirements on open-end, non-RE secured products. Unless you are referring to the credit card solicitation rules. But those normally don't apply to a standard overdraft protection product.

I think you might want to look at 226.6 - Initial Disclosure Statement. That is probably what you are looking for.

Perhaps 226.5a if you are talking about an OD or other plan that is a line of credit? It could be accessed by a debit or ATM card or exclusively so.