GM LS Seal Tight Sleeves
Darton's Seal Tight Sleeves for the Gen 4 and Gen 5 LS blocks. This allows you to take any of the listed Generation blocks and add much more strength to the block even at the bigger bore sizes. There are 3 different bore options: 3.897 bore, 4.000 bore and 4.125 bore. All of these have a max bore size of 4.187.