Yes the "corvette only" engine parts is an old wives tale, just like every set of camel hump heads (491's) are corvette heads and every high HP 327 is a corvette motor.
The thing is that the high performance 327/300 HP engine in the Impala in those early years was common with one of the corvette engines. In 64 the 327/300 Full Size Chevrolet engine came with the Carter 3720 or 3721 AFB carburetor, 3844459 intake, 3782461 "corvette" heads, and 2.5' rams horn exhaust manifolds..All comon with Corvette.
All of these components are commonly sold at the swap meets as corvette items because they are common with the corvette (and therefore bring more money). But all of them are correct for the full size chevrolet also.
The impala engines are stamped with the full size assembly suffix so you can tell if it is really a corvette or full size application if the block has not been decked.
The majority of the 327's in full size are the 250 HP versions with the rochester carb, smaller exhaust manifolds, and heads common to the 283 so most people never really associate these together.
Another cool little known fact is that 64 Impalas fitted with the 327/300 HP got an extra body/frame brace at the rear axle so you can tell if the car was originally fitted with the High Perfomance 327 (or big block 409 of course).
Alan Colvins "Chevrolet By The Numbers" for 60-64 is a good reference for these engine parts.
Tom you wrote "AFB aluminum carburetor, mechanical lifters and 2.5 " exhaust..." The impala 327/300 HP has hydraulic lifters not mechannical, only the corvette had mechanical lifters in those years. I don't know why it would state that in the manual. I'll take a looK in mine.