According to what rod you use, you may encounter rod-to-camshaft interference you will need to address. You also may have some crank-to-block interference. You will need the mains on the crank turned to fit the 350 block. You will also need the flexplate and damper from the 400.
383's are great engines - you will love them. I attached some typical dyno results so you can see expected power levels and parts required.