LA 360 vs. 5.9 Magnum

The magnums have taller lifter bores to support the roller cam. I had to go with a custom ground cam to keep my retrofit roller lifters from coming out at max lift and exposing the lifter oil groove. This was with a '71 340 block. And it is a common problem when installing a retrofit roller cam into an older block. Some people get lucky and drop one in with no problems, it just depends on how the block was cast the day it was made. The cam companies will all tell you they drop right in but that is not always the case. Plus the retrofit set up runs around $1,000 for cam/lifters. If you get a magnum you can re use the lifters and just change the cam. That right there is a good reason to go with a magnum block.