Hate to do it

I'll chime in for what it's worth. A good tight 7 1/4" will be fine for a stock 318. It will be a pegleg but that never hurt no one! Of course you can abuse any car drivetrain to the point it will break but the idea that everyone needs a Dana-60 for 300 HP is ludicrous.(and not the rapper) My stock 273 was rated at 180 HP as a 2V car with a 904 and I raced the hell out of that car with the stock 7 1/4 to no ill effect. (state cops being the exception to that deal) To upgrade from a 7 1/4 to 8 1/4 or 8 3/4 means changing the shock mount plates and u-bolts as well as shortening the driveline and that is potentially just the start.
Cheers and happy mopar motoring--------------DR--------------:D