I have to agree that the 7 1/4 rear should hold up to a mild 318. We have one in my Son's "73" 4 door Dart and I'm not concerned it will break anytime soon. There are two good ways to upgrade in my opinion. The easiest is to get a 8 3/4, either complete or piece it together. The 8 3/4 is strong, has the good adjustable rear bearings that will last a lifetime, has the small bolt pattern, and has a removable carrier that makes a gear change 1/2 hour away. Next, if you do not have 10 in front drum brakes, swap the Kelsey Hayes small pattern disc brakes on the front. I've done this on two of my cars and am very pleased with the results. The other way to go, since you have front drum brakes (9 in?), is to swap the big bolt pattern disc brakes on the front. Then an 8 1/4 rear. Obviously this can be done in any order. The main point is to think ahead to what you want to end up with, and work toward that goal. I'm assuming Chrysler parts, the same bolt pattern front and rear, and the simplest in the long run.
