1. Can I cheat and say magnum 360? In an a body specifically I dont see the 383 being worth the difference in cost and size.
2. Same. 360 magnum.
3. Same 360 magnum. Every 383 block will need machine work. That's money I won't spend on a 5.9 block that will let me buy better heads.
4.383. Bigger is better and better flowing heads are available
My rule of thumb is bang for buck is always magnum 5.9 but if I were a legit racer or I need torque for a truck bigger is better.