Potential project Barracuda

A 360/904 combination would probably be the cheapest and easiest way of getting 300+ horsepower and is a relatively easy install. You'll need to decide early on what brakes, wheels, and bolt pattern you're going to use before you buy a rear axle or disc brake package. There are pluses and minuses to various options. With that horsepower, I would want at least an 8 3/4 rear axle assembly. The existing 7 1/4 is a grenade with the pin almost out and hanging on by a thread. An 8 1/4 is cheaper and easier to get over an 8 3/4, and comes with the 4 1/2" bolt pattern, but, it's not as strong and has a poorer designed axle shaft setup. It's also harder to swap gears if you chose to do so at a later date. A-body 8 3/4's are kind of pricey so, finding one out of a different model and having the housing narrowed to fit an A-body can sometimes be the way to go. That way you can choose which 3rd member you want to use, and whether you want to keep the small bolt pattern wheels or change to the big bolt pattern and bigger brakes. If you happen to stumble over a stock A-body 8 3/4 sure grip rear, that wouldn't be a bad thing, but, it would have the small bolt pattern wheels. Unless you change to an aftermarket axle shaft, you would probably want to stay with the small bolt pattern brakes up front too, so you don't have to carry two spares. That would mean rounding up a complete Kelsey Hayes A-body disc brake changeover.....not an easy task either. Since the car isn't going to be stock, I'd find a good donor car with the brakes and rear end I want and modify things as necessary. You might even find one with the engine/trans you want too. Check with your local wrecking yards or online ads for a donor car. Sometimes you can get a rust bucket cheap that has a good drivetrain.