It kind of depends on the sleeves, but in most cases it is definitely not OK. Generally two adjacent sleeves in a block will split the block at the deck eventually, leading to head gasket failure and coolant in the oil. There are some engine builders who will sleeve down a 427 block to 390 bore size, but taking a minimum amount out of the stock 427 bore. What is the bore size of the block? If it is stock 427 size (4.23"), or bigger, I think that block is headed for failure.