Also not an attorney, but it’s my understanding that a 501cX organization can only fiscally sponsor projects that fall into the same IRS designation. For example, 501c3 organizations can fiscally sponsor other c3-type organizations. Same for c4 organizations. While I have not come across many c7-type organizations seeking fiscal sponsorship, my understanding is that they’d have to seek that fiscal sponsorship from an existing c7.

But, as a counterpoint, if the organization has already has c7 status from the IRS, what’s the benefit of it becoming fiscally sponsored by another organization?