I bought a 64 Barracuda in 1970. 273 4bbl, hiring, 780 dual feed, fenderwell headers and weld on bars holding down a 59 Fairlane 9"rear.
Put a D Dart cam in it and beat the **** out of it for 3 years. Street raced over a 1000 times.and only got beat 3 times.
That car was a monster for what it was.
Now have a 65 that was a /6 factory 4 speed. Pulled the 6 and built a 273 and installed it. Its only a low compression motor but still a lot of fun. With only a 7.25 rear, there is NO racing. Still looking for another Fairlane rear.
Buy or build a 273, they're great little.motors.