They can be used in all Ford FE engines 352, 360, 390, 410, 427, and 428 if you tap the holes. They greatly increase the strengthen and rigidity of the block as well as eliminate the possibility/danger of the press in plugs blowing out at some inopportune time. Block "MUST" be tapped to install (1-1/2" NPT). Sold in a set of 6.