Greenfield, you say? Here's my sicko mode suggestion (red at/above grade, blue u/g) if no existing rail ROWs can be utilized.
Put grand central station terminus stretching from 103 to 102 ave between 97th to 95th, plus extended over 97th st where the law courts building is, utilize those existing pedway connections to Churchill, and have direct access to Quarters VLSE station.
The stretch down Baseline is probably elevated. Replace the Dawson with a nice combined vehicles on the bottom rail on top bridge. Old coal mines a major concern near the Rowland Rd portal, and McNally Highschool is probably demolished (but it's having geotechnical issues already). Overall fairly minimal expropriation required, mostly in Fulton and Riverdale north of Rowland Rd.
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