A couple of questions about my fender tag!

1974 only had a 150HP single exhaust and a 170HP dual exhaust 318 engine. The 230 HP 318's were in '71 and earlier vehicles. I would bet your transmission is a 904. Check the pan, if it's square with a corner cut off, it's a 904. If you want to change to a low gear ratio (higher numerically) you'll need to change the carrier along with the ring and pinion. You can keep the axle housing and brakes. A good donor is a van or pickup. They're much more likely to have a sure grip and low gears. Grab everything....spacers, adjusters, bearings, Etc. Unless you're an expert, have a good rear end shop set it up for you. It takes some know-how and special tools to do it right.
Thanks, Mark