This is a first time repair: NorthStar 2000 head bolt M11x1.5 kit includes all the tools and 10 inserts P/n 11155 are included, 20 inserts required to do entire block. In 2000 GM changed the head bolt depths to 35mm upper bank and 51mm lower bank.  In the year 1999 and earlier the block was 1 depth 35mm all hole upper and lower bank. This is measured from top of the block to the first starting thread