all big blocks have short and long have two size and the new roller cam engine have a different size. the stock sizes is 8.280 and9.250 this is not for the new roller engine or tall deck they takes a different size to so do the retro roller cam to the mark4 and5 takes a different size to. comp makes them for this and they make them in 5/16 3/8 7/16 tube for HO use go for the 3/8 tube and 3/8 guide plates a good set this is no place to get cheap