This is news to me so bare with me if it is old news to you.  I recently purchased the entire original drivetrain from a 1964 Nova SS V-8 4spd.  At the time of purchase, I was content to install the parts from rad to rearend just as they came from the factory.
While in York, PA, NNN headquarters, I picked up a 64 Nova SS to be delivered to Kansas.  At the same time, I picked up the above drivetrain that had been retained from a 64 Nova SS sold to a buyer that planned to build a "Hot Rod" and had no use for the 283, 4 spd, posi drivetrain. 
While loading the parts, Wayne made mention to me that this was a late 64 build and therefore could be overbored to a 327 displacement.  This tidbit really intrigued me as I had been wondering how I could get more HP from these parts without giving up the original appearance and parts.  He said the block was a 721 and that block was used in 65 & 66 for the Nova SS 327 cars.  The block can take a .125 overbore and when used with a 327 small journal crank, it is 327 ci displacement.
This opened up a whole new list of possibilities for me in terms of combinations of components I could use resulting in nummerous cubic inch and HP output.
I have since completed the 3,000 mile trip and arrived home with a California 63 Nova SS and a trailer full of parts.
I have the block on a motor stand and it is indeed a recessed oil filter 3790721 with a 283 bore and engine pad stampings of F0927CF.  I forgot to write down the date code but the application code shows it as a 64 283 4 spd.  I think the F is for Flint and 0927 is Sept. 27, 1964 build date for the car.
Funny thing is I started working at the Flint Engine Plant building 283, 327, 6 & 4 cyl motors in Oct. 1964.  My guess is this block came down the line about a month prior to my employment.
I'm posting this information because I don't know how many other people know that some of the 283 blocks used in the 1964 Nova SS V-8 builds were actually 327 blocks and can be rebuilt as a 327.  I also bought a 4bbl intake manifold and NOS AFB carb while in York and along with the 327 crank I located, the only questions left are what cam and heads to use.  Most of the heads seem to have 1.72 intake valves even on some of the 327's but I think I will continue to look for a set of 1.94's from the era.  I do not want to run over 10 to1 comp. so flat tops will be used and I'm thinking about a 300 hp 327 cam or possibly an L-79 grind.
What do you think??