Join Date: Jan 2019
Location: Sedgwick, Kansas
While there are plenty of guys with 351's in their early 'Stangs, it is a pretty snug fit. It's also about 80 lbs heavier than a 302. If you want massive amounts of cheap power, and mostly going in straight lines, the 351 would be fun. For drag racing, there's no question: a stock block 351 can handle up to around 750 horses before it has problems, while the 302's limit is somewhere around 500. Changing spark plugs, or delivering good handling will be more challenging with a 351.
The 302, especially with some good heads, can definitely deliver enough power to overwhelm the rear tires too. With aluminum heads and intake, you can get the weight down far enough to make even mild suspension mods really impress. In a light first gen Mustang, there's nothing wrong with small block power at all. Don't forget - with your car's light weight, even 200 horsepower can be a LOT of fun. 300 is pretty outrageous. You don't have a 3500 lb boat to haul around - which is why you can get by with a nice mild build and still annihilate some tires with ease.
If you want a brutal brawler, go with the 351. For more refined handling to go with the performance, I'd stick with a 302 based build.
"No matter what you are, be the best one you can." -Abraham Lincoln