What cam to use in a 318

Your Magnum heads have quench, correct? With 9.2:1 CR, I would choose a modern cam profile and run 87 fuel. I do not expect you to have a problem with that. As recommended, talk to Jones Cams and Oregon Cams. Have your engine information to send them. The more infirmation you fill in the better they can recommend the appropriate cam for your intended usage.