Thinking outside the box

are these new hi-tech gm heads a true bolt on for your typical 70's 350?

No they do not.
Even to retro fit them on the GM Gen III & IV engines they need new offset inlet rockers (~$100.00 for all) a special L76 intake manifold (~$450.00), and a special head gasket ($ is a wash on this one considering any new head replacement will need a new gasket).