Hi.
I've modified the code and schematic to check for the value on pin 6 (PD4) of the ATMEGA328 (ie. ARDUINO DIGITAL PIN 4) at startup.
If it is low then the chip now displays using NTSC timing. Leave disconnected for PAL.
Currently, it uses information that I took from the datasheets. I am waiting for an AY-3-8500-1 NTSC version of the original chip to arrive. When I get it, I will tweak values if necessary.
Latest code and schematics online.
http://searle.hostei.com/grant/AVRPong/index.html
Any probs or queries, please feel free to contact me.