Holding a 403b1 annuity contract in a 403b7 custodial account

[IHC]

Would appreciate thoughts on whether a trust company could have one custodial account agreement for a 403b plan that holds both 403b1 annuity contracts and 403b7 custodial accounts.  My thought is that the annuity contract has to be held in a separate custodial account (or in no custodial account at all) or the tax-exempt status of the 403b7 custodial account is at risk.  Is there anything I am missing? Any nuance in the regulations I've overlooked?  1.403(b)-8(d) seems very clear on this point.  Would a master custodial account that holds the b7 assets in a subaccount separate from the b1 annuity contract work?

Also, I'd appreciate thoughts on whether a 403(b)(7) custodial account agreement must have what I call "quasi-plan language" in it, i.e., language that states deferrals won't exceed 402g, distributions won't be made at impermissible times, etc.  The large 403b vendor agreements seem to all contain this language, but is it absolutely necessary if the plan document has the requisite language?  Does it depend on whether the custodial account agreement incorporates the provisions of the plan?

Thanks in advance for any insights/feedback.