The 5.7 rods aren't too important. They will only show minimal gains. I would recommend them only if you are starting from scratch.
A 400 should make 350hp easy with your cam.
If you went to 2.5" exhausts your engine would make even more power. 2 1/4" is small for a performance 400. It isn't like a 350. That extra 1/4" will make a big difference.
Of course, an aftermarket head will be needed if you want to get to the 400hp range easily.
I use the Percy's aluminum gaskets. They work well. I have even reused them and still had them seal.