318 magnum question (brainfade)

an old guy i know has a 73 swinger.i bought it for 800.00 for some of the parts it came with. msd billet dist eddy air gap x heads etc. anyway i sold it to him for 800.00 as a roller. he has put in 4 or 5 engines and none have lasted very long. most grind the cam to nothing.i call him bad luck chuck.he took it to his moms in monterey and itdid it again.i told him to find a 318 magnum and it should last . he already has a set of magnum heads (new) and a magnum air gap. i told him he just needs a shortblock.so he needs the hughes cam extention for the fuel pump eccentric. and reuse his timing cover, pan but which balancer ? la or magnum?:violent1: