I happened to notice your screen name FRiend, and it reminded me of an old friend in high school who indeed drove a ‘64 Impala SS, with the rather unorthodox (to my thinking) drivetrain of 409/340 hp and *Powerglide*. Even with that 2-speed transmission it could really smoke ‘em up.
Good times!
Mine’s got a 327 with the powerglide. Those transmissions had a bad effect on gas mileage but they were very sturdy and trouble-free. In fact, with a few relatively cheap mods, they’re still used in some dragsters.