Looking for an anto od trans for a 66 /6 Valiant

The short answer is nothing. Nothing is a bolt in and nothing will fit without major floor tunnel surgery and cross member surgery. You might check with the guys at Gill Welding to see if they offer some kind of adapter plate. They are Mopar and slant 6 guys. That would be my first step. Getting "whatever" transmission I chose to bolt to the engine. From there, it's all pretty much labor.