I would also add that on the Holley website there are PDF documents with drawings that do a really good job of explaining the differences between the different types of brackets. In addition to that there are instructions that clearly show and explain what's going on with them and parts lists of all the required components with multiple vendor part numbers that are very helpful in procuring the needed parts including small fittings and such to make the install much easier. They have really done a good job with this product line.