ALEC was definitely part of the Heritage Foundation in the 1970s. They stole it out from under the woman who'd founded it because they wanted a non-profit. Then they used it for campaign lobbying in violation of its non-profit status.
As for the State Policy Network, an analysis titled Target San Diego -- which was no longer online the last I looked -- has this to say about their origins:
While the American Legislative Exchange Council focuses on coordinating the right's state legislative agenda by networking politicians and corporate interests, the State Policy Network (SPN) was created to support the growth, organizational capacity and policy sophistication of state-based conservative think tanks. Conservative leaders understood by the mid-1980s that to effectively move their agenda through the states and cities they would need a policy and advocacy apparatus to reinforce the efforts of national umbrella groups such as the Heritage Foundation and American Enterprise Institute and complement the legislative drafting and networking activities of ALEC.
Particularly after devolution of Federal functions to the states became a cornerstone of conservative strategy in the 1990s, this meant strengthening existing state think tanks by developing their organizational structures, development operations and grassroots mobilization efforts. It has also meant creating new think tanks where none previously existed, particularly in the "blue states." . . .
Now based in Richmond, California, SPN grew out of an informal network of state think tanks called the Madison Group that was organized in 1986 and then taken under the wing of the Chicago-based Heartland Institute, one of the largest groups in the network. It was formally established as an independent organization in 1992 under the leadership of its longtime board chair, the late Thomas Roe. . . .
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