I bought a 415 rotating assembly from Speed-O-Motive and it works great, I highly recommend them. The block will need to be notched in the oil pan area. The longer stroke crank will need deeper notches to clear the counter weights. Since the 400 is externaly balanced you will need a balancer and flywheel/flexplate for a 400 CID chevy motor as well to complete the 383 kit. They clearance the rods for you in case your running an aggressive cam. They can also cermaic coat your pistons for a small additional fee.
I started with nothing and I still have most of that left! - <a target="_blank" href=http://www.echobit.com:81/k5/> Pictures</a>