A 427 engine *might* fit in a 1970 Cutlass, but it's not a straightforward swap and will require significant modifications. The 1970 Cutlass wasn't designed for an engine that large. You'll likely need custom headers, possibly engine mounts, and potentially modifications to the firewall and possibly even the subframe to make it fit. The transmission will also need to be compatible with the 427's torque.
In short, while *physically possible* with enough custom fabrication, it's not a simple bolt-in affair and is a project best undertaken by someone experienced in engine swaps and fabrication.
