Well, I found that : 
  
public class BlockStairs extends Block 
{ 
    private static final int[][] field_150150_a = new int[][] {{2, 6}, {3, 7}, {2, 3}, {6, 7}, {0, 4}, {1, 5}, {0, 1}, {4, 5}}; 
    private final Block field_150149_b; 
    private final int field_150151_M; 
    private boolean field_150152_N; 
    private int field_150153_O; 
    private static final String __OBFID = "CL_00000314"; 
  
Which I believe sets the block bounds.. But I don't know what to put instead of "field_150149_b" and so on .. Can someone help me ?