Classic/Antique Car Repair: 1964 chevy engine, chevy impala, 1964 chevy impala

Question
Hello Mr.Wilczynski

I've got a 1964 Chevy Impala, and I'm trying to find the info on the engine. Decoding the serial number on the car states it should have a 327 and a few old car guy friends look at it and say "it's a 327" without being able to quite tell me why (supposedly because you don't put ram's heads on a 289).
The casting number (engine casting date/suffix) on the front passenger side of the car reads 854629658, which is not near anything shown on the websites I've found. Do you have any reference material that might say what this serial means? Unfortunately the car is a good drive away right now, so I am unable to get the casting number off the driver's side rear of the engine.

Any help you can give would be greatly appreciated.
Thank you for your time.

Answer
I'm sure you mean "283", not "289", and these had the ram's head exhaust manifolds, too.

That casting number should begin with a "3", not an "8", and most 283 and 327 heads from that vintage have the same casting number.

The only way to really tell is by finding the block casting number.

--Paul