Info on 74 Dart Sport

If that's a real Dart 360 Sport, with the original engine, that's a pretty nice package. It has bigger valves and better heads than other 360s. Hardened exhaust valve seats, too, ready for unleaded gas.
Remember, that 250 HP is net, whereas just a couple years earlier horsepower was rated in gross numbers. Gross HP on that 360 should be an honest 275 or better. Check for a code E58 on the data plate on the driver's side inner fender. That should be there if the car was built with a high perf 360.
Check it over well. Take a friend who knows Mopars with you. Check to see if the numbers on the oil pan rail of the block match the VIN tag. Unless you're rail thin and bird chested, you'll need a jack to be able to see it. That will tell you if the engine block is original to the car. If it doesn't match, you'll need to investigate further to see what is actually in there. It could be a 2bbl 360 or 318. They'll run, and can be made to run well, but you're starting with less, and the price should reflect that. If the seller tries to discourage you from checking any of those things, he may be trying to hide something. Never a good sign.
The Dart 360 Sport was, along with the 360 Duster, the top performance A-Body in 1974. Definitely a collectible car. Good luck.