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 ?