No, it's 1981 (Defender was released in February that year). I believe Bower was working at Williams at the time, contemporaneous to Defender (in the next windowless lab). He showed it to Eugene Jarvis at one point, who laughed and said "I don't even have a reverse button on my game and that's still considered too complicated. You're nuts." (This is true - Defender originally only allowed you to fly forward). The reason I haven't mentioned either direct quotes from Eugene or the name 'Williams' is that (cough) Lawyers (cough, splutter). I redacted them. :-)
As for the 6503, somewhere between '75 and '81, someone was doing weird stuff with the 6502. I am presuming a former cult member.
Bower went missing at the end of 1981, but is believed to have moved to Sinneschlosen, although that can't be confirmed, of course. Some believe Polybius IS just Spellrazor with a re-skin (hence the short timeframe), but those people are probably fools.