Not an issue if the 318 crank pilot hole is deep enough. If you don't get a finished crank (pilot hole machined for a manual trans pilot bushing) just use the Magnum pilot bearing. Your flywheel will fit just fine. Depending on blocks sometimes motor mount brackets need to be modified to fit. It's a matter of how many bosses are on the block and where they are located. Most 273's have three bosses on each side with a bracket to match. Some 318's also have three, but, a different three, so brackets have to have ears cut and added as necessary. Some later blocks have all four bosses.