Please stop buying parts until you have known measurements of what you already have. LY rods are 6.760 CTC length. Stock 383/400 B motor rods are 6.358(ish) CTC.
I'm going to bet the block will require between 010 and 020 to clean up square. The last two 400 blocks I did cleaned up at 9.965 deck height. This is to your advantage. If the rods are stock 6.358 length, the KB400 is a good choice as long as the rings are set using the proper gap, which is larger for the hyper explosive pistons. S/F.....Ken M