Plain old dextron/mercon ATF. Most trans fluids are now formulated to fit any make or model. back in the day you had to get dextron for GM/chrysler and ford atf for ford lincoln and mercury. Now most fluids are just labled ATF one size fits all.
Good luck with your "land barge" I used to have a 70 and later a 78 Newport..great cars, room for 8 and plenty of legroom LOL