There are some minor differences in the LT4 rotating assembly but none really worth mentioning.
400fwhp can be easily had without touching the heads. I would go with an AI cam and cam kit, stock reconditioned crankshaft and rods and a good Mahle piston (hypereutectic would be fine in this instance). Have the cylinders bored .030" to clean up the cylinder walls. Add on top of that a good mail-order tune and a set of headers (I don't see them listed in your mod list) and you'll have a strong running car.
