I had a 400 with 5.7 rods in my el Camino. Would be my choice again if i was going to use a sbc. But a 383 ain´t bad, would be my second choice.
If'n it was me ,I would get solid prices on each option, I think you will find that a 383 is a real bargain for the money spent . After all if you are street driving it the extra power may be wasted due to lack of traction for the 396.
383 with 5.7 rod you can use stock cam( most of the time) still need to clearance the pan rail. Pistons are reasonable cost. 383 6 inch rod, you're buying aftermarket rods get the ones set up for strokers on the journal end to reduce pan rail clearance needed. pistons available, will be more expensive. 396, aftermarket rod, youll need a small base circle cam and ***ociated valvetrain. Just depends on what you have to work with and how much you want to spend on aftermarket parts. unless you're ***embling this yourself, the machine shop bill on clearancing the pan rails and multiple mock up fits of the rotating ***embly can get expensive. A 5.7 rod 383 is a very solid engine, proven for years.